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PREFACE .

T HE rapid progress o f di scovery in the lastfew years has created a very general i nterest inbacteria . Few peopl e who read cou ld be foundtod ay who have not some l i tt le idea o f theseorgani sms and thei r re lation to disease . It i s

,

however,unfo rtu nately a fact that i t i s on ly thei r

relation to disease which has been impressed uponthe publ ic. The very word bacteria

,or microbe

,

conveys to most people an idea of evi l . The lastfew years have above al l things emphasized theimportance o f these o rganisms i n many relationsen ti rely independent of disease, bu t thi s side ofthe subject has not yet attracted very generalattention , nor does i t yet appeal to the readerwi th any special fo rce. I t i s the pu rpose of thefol lowing pages to give a brief outl in e o f ourknowledge of bacteria and thei r importance inthe world

,incl uding not on ly thei r wel l - known

agency in causing disease,but thei r even greater

importance as agen ts i n other natu ral phenomena .

I t i s hoped that the resu l t may be to show thatthese organi sms are to be regarded no t primar i lyi n the l ight of enemies

,bu t as friends

,and thu s

to correct some of the very general bu t erroneousideas concerning thei r re lat ion to ou r l i fe.

MIDDL ET OWN, April 1 , 1 897.

5

C ONT ENT S.

CHAPT ER

I.—BAC TERIA ‘

AS PLANT S

Histo rical.—Fo rmo f bacteria —Multiplicatio n O f bacteria.

—Spo re fo rmatio n .—Mo tio n .

—Internalstructure .

Animals o rplan ts i—C Iassificafiom—Variatio n .—Where

II. MISC EL LANEOUS UsEs O F BAC T ERIA IN THE ART S.

Maceratio n industries. L inen . Jute. HemSpo nges. L eather. Fermen tative industries. ine

gar.—Lact ic acid.

—Butyric acid—Bacteria in to bacco

curing.—T ro ublesome fermen tatio ns.

III.—BAC T ERIA IN T HE DAIRY

So urces O f bacteria in milk—Effect O f bacteria o n

milk.—Bacteria used in butter making.—Bacteria in

cheesemaking.

IV.—BACTERIA IN NAT URAL PRO C ESSES

Bacteria as scavengers —Bacteria as age n ts in Nature‘

s

fo o d cycle .—Relatio n O f bacteria to agriculture .

—Spro uting Of seeds.

- T he silo —T he fertility O f the so il.—Bacteria as so urces O f tro uble to the farmer.

—C o a1 fo rmatio n .

V.—PARASIT IC BAC T ERIA AND T HEIR RELAT ION T O

DISEASE

Method O f producing disease—Patho genic germs n o t

strictly paras itic—Patho gen ic germs that are true

gSim—What diseases are due to bacteria.—Varia ility

7

8 T HE ST ORY OF GERM L IFE.

P. sG B

O f patho genic po wers.—Susceptibility O f the individual .

Reco very from bacterio lo gical diseases. Diseasescaused by o rganisms o ther than bacteria.

VL—METHODS OF C OMBAT ING PARASITIC BAC T ERIA 165

Preventive medicine.—Bacteria in surgery .

—Preventio n by ino culatio n .

—L imits o f preventive medicine .

C urative medicine .—Drugs. - Vis medicatrix nature .

An tito xines and their use.-C o nclusio n .

T HE ST ORY O F G ERM L IFE.

CHAPTER I .

BAC T ERIA AS PL ANT S .

DURING the last fi fteen years the subj ect o fbacteriology ! has developed with a marvel lousrapidi ty . At the beginn ing O f the ninth decadeO f the cen tury bacteria were scarcely heard ofoutside O f scientific C i rcles

,and very l i ttle was

known abou t them even among scientists . T O

day they are almost household words, and everyone who reads is beginn ing to recognise thatthey have important re lations to hi s everydayli fe . The organisms cal led bacteri a comprisesimply a smal l class of low plants

,but thi s smal l

grou p has proved to be of such vast impo rtancein its relat ion to the world in general that i tsstudy has l i ttl e by l i tt le crystal l i zed into a scienceby itsel f. I t i s a somewhat anomalou s fact thata special branch O f science

,interesting such a

large number O f people,shou ld be developed

around a smal l group of lo w plan ts . The importance O f bacterio logy is n o t due to any importancebacteria have as plants o r as members o f thevegetable kingdom

,but so le ly to their powers O f

T he termmicro be is simply a w o rd which has b eenco ined to include all O f the micro sco pic plan ts commo nly included under the terms bacteria and yeasts.

9

1 0 T HE ST ORY O F GERM L IFE .

producing profo und changes in Nature . There i sno one fami ly O f plants that begin s to comparewith them in importance . I t i s the O bj ect of th iswork to po in t out briefly how much both O f goodand i l l we owe to the l i fe and growth O f thesemicroscopic organisms. As we have learnedmore and more of them during the last fi fty years

,

i t has become more and more eviden t that thisone l i ttle class O f microscopic plants fil l s a p lacein Nature ’s processes which in some respects balances that fil led by the whole O f the green plan ts .Minute as they are, thei r importance can hardlybe overrated

,for upon thei r activ it ies i s founded

the contin ued l i fe O f the animal and vegetablek ingdom . For good and for i l l they are agentsO f neverceasing and almost un l imi ted powers .

H IST O RIC A L .

The study O f bacteria practical ly began withthe use of the micro scope . I t was toward theC lo se of the seventeenth centu ry that the Dutchmicroscopi st

,Leeuwenhoek

,working with h is sim

ple lenses,first saw the organisms which we now

know under this name,with su fficien t clearness

to describe them . Beyond mentioning thei r existence , however, his observations told l i tt le o rnoth ing. Nor can much more be said O f the studies which fo l lowed during the next one hundredand fifty years. Duri ng thi s long period many amicroscope was tu rned to the Observation o f theseminu te organisms

,but the majori ty of Observers

were contented with simply seeing them,marvel

l ing at their minu teness,and u ttering many excla

mations of astonishmen t at the wonders of Natu re .

A few men O f more strict ly scien tific natu res paid

BAC T ERIA AS PLANTS. I I

some atten tion to these l ittle organisms. Amongthem we shou ld perhaps mention Von G leichen ,Mtiller

,Spal lan zani

,and Needham. Each O f

these,as wel l as others

,made some contributions

to our knowledge O f microscopical l i fe, and amongother organisms studied those which we n o w cal lbacteria . Speculations were even made at theseearly dates o f the possible causal connection O f

these o rganisms with diseases,and for a l i tt le the

medica l profession was interested in the sugges

t ion . I t was impossible then , however, to Obtainany ev idence fo r the tru th O f thi s specu lation, andi t was abandoned as unfounded, and even forgotten completely

,u nti l revi ved again about the mid

d le o f the presen t cen tu ry . During this centu ryO f wonder a su fficiency O f exactness was, however

,i ntroduced into the study O f microscopic o r

ganisms to cal l fo r the use O f names, and we findMul ler using the names O f Monas, Proteus, V ibrio,Baci l lu s

,and Spiri l l um

,names which sti l l con tinue

in u se,al though commonly with a di fferen t sign ifi

cance from that given them by Mul le r . Miillerdid indeed make a study su fficient to recognisethe several di sti nct types

,and attempted to clas

sify these bodies. They were not regarded as ofmuch importance

,bu t simply as the most minu te

o rganisms known .

Nothing of importance came from thi s work,

however,partly because O f the i nadequacy of the

microscopes O f the day,and partly because of a

fai l u re to u nderstand the real problems at i ssue .

When we remember the min uteness of the bacteria,

the impossib i l i ty O f studying any one of them formore than a few moments at a time—on ly so long

,

i n fact,as i t can be fo l lowed u nder a microscope ;

when we remember, too, the imperfection O f the

1 2 T HE ST ORY OF GERM L IFE.

compound microscopes which made high powerspractica l impossibi l i t ies ; and , above al l , when weappreciate the looseness o f the ideas which pervaded al l scien ti sts as to the necessi ty o f accurateObservation in distin ction from in ference

,i t i s no t

strange that the last - C en tury gave us no knowledge O f bacteria beyond the mere fact O f the existence O f some extremely min u te organisms indi fferent decaying material s. Nor did the presen tcentu ry add much to th is unti l toward its midd le .

I t i s true that the microscope was vast ly improvedearly in the cen tu ry, and since thi s improvementserved as a decided stimu l us to the study of micro sco pic l i fe, among other organisms studied,bacteria received some attention . Ehrenberg

,

Duj ardin,Fuchs

,Pe t ty , and others left the im

press O f thei r work upon bacterio logy even befo rethe middle O f the centu ry . I t i s true that Schwannshrewdly drew concl u sion s as to the relation O fmicroscopic organ isms to various processes O f

fermentation and decay— conclusions which,al

though not accepted at the t ime, have subse

quently proved to be co rrect . I t i s true thatFuchs made a carefu l study of the in fection O f

blue milk,

” reaching the correct conclusion thatthe infection was caused by a microscopic organism which he discovered and carefu l ly studied.

I t i s true that Henle made a general theory as tothe re latio n o f such organ isms to diseases

,and

poin ted out the logical ly necessary steps in a demo nstratio n O f the causal connection between anyorgani sm and a disease . I t i s true also that ageneral theory O f the productio n O f all k inds O f

fermentation by l ivi ng organisms had been ad

vanced. Bu t al l these suggestion s made l i tt l eimpression . On the one hand

,bacteria were not

BAC T ERIA As PLANT S . 3

recognised as a C lass O f organisms by themselves—were not

,i ndeed

,distingu i shed from yeasts or

other minu te animalcu lae . Their variety was notmistrusted and thei r sign ificance not conceived .

As microscopic o rgan isms,there were n o reasons

fo r considering them of any more importancethan any other smal l animals or plants

,and thei r

extreme min u teness and simpl ici ty made them O f

l i tt le in terest to the micro scopist . O n the otherhand

,thei r causal connection with fermentative

and putrefactive processes was en ti re ly obscuredby the overshadowing weight o f the chemist Liebig

,who bel ieved that fermentation s and putre

faction s were simply chemical processes . Liebigin sisted that al l albuminoid bodies were in astate of C hemical ly u nstable equ i l ibr ium, and i fl eft to themselves wou ld fa l l to pieces wi thoutany need of the action O f microscopic organisms.The force of L iebig

’

s au thori ty and the bri l l iancyo f h is exposi tions led to the wide acceptance O fh is v iews and the temporary O bscuri ty O f the rel ation of microscopic o rgani sms to fermentativeand pu trefacti ve processes. The Objections toL iebig

’

s v iews were hardly noticed, and the forceO f the experiments O f Schwann was si len t ly ignored . Unti l the six th decade of thi s cen tu ry

,

therefore,these organi sms

,which have since be

come the basi s of a new branch of science,had

hardly emerged from O bscu ri ty . A few microsco pists recognised thei r existence, j ust as theydid any other group of smal l animals or p lan ts

,

but even yet they fai led to look upon themasforming a distinct group . A growing number O fobservation s was accumulating

,pointing toward

a probable causal connection between fermentative and putrefactive processes and the growth of

1 4 T HE ST ORY OF G ERM L IFE .

microscopic organ isms ; but these observation swere known on ly to a few

,and were ignored by

the majority of scientists.I t was Louis Pasteur who brought bacteria to

the front, and i t Was by his labou rs that these o rgan isms were rescued from the obscurity of scient ific publ ication s and made obj ects of general andcrowning in terest . It was Pasteu r who first successfully combated the C hemica l theory o f fermentation by showing that albuminous matterhad n o i nherent tendency to decomposition . I twas Pasteur who fi rst C learl y demonstrated thatthese li tt le bodies

,l ike all larger animal s and

plants, come in to ex istence on ly by ordinarymethods of reproduction

,and not by any spo n ta

neo us generation,as had been earl ier C laimed .

I t was Pasteu r who first proved that su ch a common phenomenon as the souring of mi lk was produced by microscopic organi sms growing in themi lk . I t was Pasteur who fi rst su cceeded in demo nstrating that cer tain species of microscopic o r

gan isms are the cause of certai n diseases, and insuggesting successfu l methods o f avoiding them .

Al l these discoveries were made in rapid succession . Within ten years o f the time that h is namebegan to be heard i n thi s connection by scien

t ists,the subj ect had advanced so rapidly that

i t had become evident that here was a newsubj ect of importance to the scien tific world

,i f

not to the publ ic at large . The other importan tdiscoveries which Pasteu r made i t i s not our purpose to mention here . His C laim to be co n sid

ered the founder of bacterio logy wi l l be recogn ised from what has al ready been mentioned .

I t was n o t that he fi rst discovered the organisms,

or fi rst studied them ; i t was not that he first sug

BAC T ERIA As PLANT S. 5

gested their causal co nnectio n wi th fermentationand disease, bu t it was because be fo r the fi rst t imeplaced the subj ect upon a fi rm foundation by proving with rigid experiment some of the suggestionsmade by others

,and in thi s way turned the atten

tion o f science to the study o f micro - o rganisms .After the importance of the subj ect had been

demonstrated by Pasteur,others tu rned thei r at

tention in the same di rection,ei ther fo r the pur

pose o f verification or refutati on o f Pasteu r ’sviews . The advance was not very rapid

,however

,

si nce bacterio logical experimentation proved to bea subject o f ex traordinary difficu lty . Bacteriawere not even yet recognised as a group of o rgani sms disti nct enough to be grouped by themselves

,

but were even by Pasteur at fi rst con founded withyeasts . As a disti nct

,group of organ isms they

were first di stingu ished by Hoffman in 1 869, sincewhich date the term bacteria

, as applying to thisspecia l group of organisms, has been comingmore and more in to use . So difficu l t were theinvestigations

,that for years there were hard ly

any investigators besides Pasteur who cou ld successfully handle the subj ect and reach concl usions which cou ld stand the test of time . For thenex t th i rty years

,although investigato rs and ih

vestigatio ns contin ued to increase , we can findl i tt le besides di spu te and confu sion along thi sl ine . The difficul ty of obtain ing for experimen tany one kind o f bacteria by i tsel f

,unmixed wi th

o thers (pure cu l tures) , rendered advance a lmostimpossible. So con flicting were the resu lts thatthe whole subj ect soon came in to almost hopelessconfusion

,and very few steps were taken upon

any su re basi s. So difficu l t were the methods,so

contradicto ry and confusing the resu lts,because

1 6 THE ST ORY OF G ERM L IFE.

of impu re cu ltures,that a student of to day who

wishes to look up the previou s discoveries inalmost any l i ne of bacterio logy n eed hardly goback of 1 880

,since he can almost rest assured

that anything done earl i er than that was morel ikely to be erroneou s than correct .The last fi fteen years have

,however

,seen a

wonderfu l C hange . The di fficu l ties had beenmostly those of methods of work

,and with the

n inth decade of the centu ry these methods weresimpl ified by Robert Koch . This simpl ificationof method for the first time p laced this li n e ofi nvestigation within the reach of scien tists whodid n o t have the geni u s o f Pasteu r . It was nowpossible to get pure cu l tu res easi ly

,and to Obtain

wi th such pure cu ltu res resu l ts which were un i

form and Simp le . I t was.

n o w possible to takesteps which had the stamp of accu racy uponthem

,and which further experiment did not dis

prove . From the time when these methods werethu s made manageable the study of bacteria increased with a rapidi ty which has been fairlystart ling

,and the i nformation which has accumu

lated is almost formidable. The very rapidi tywith which the investigation s have progressedhas bro ught considerable con fusion

,from the fact

that the new discoveries have not had time tobe properly assimi lated i n to knowledge . Today many facts are known whose significance i ssti l l u ncertain

,and a C lear logical discussion of

the facts of modern bacterio logy is not possibl e .

But su fficient knowledge has been accumu lated anddigested to Show u s at least the direction alongwhich bacterio logical advance is tending

,and i t

i s to the poin ting ou t o f these di rections that thefol lowing pages wi l l be devoted .

BAC T ERIA AS PLANT S. 1 7

WHAT ARE BAC T ERIA ?

The most interesting facts connected with thesubj ect o f bacterio logy concern the powers andi nfluence in Nature possessed by the bacteria .

The morpho logica l side of the subj ect i s in teresti ng eno ugh to the scientist

,bu t to him alone .

S t i l l,i t i s impossib l e to attempt to study the

powers o f bacteria wi thou t knowing something ofthe organisms themselves. To understand howthey come to play an important part in Natu re ’sprocesses

,we must know fi rst ho w they look and

where they are found . A short con sideration o fcertain morphological facts wi l l therefore ben ecessary at the start .

FORM O F BAC T ERIA .

I n shape bacteria are the simplest conceivableSt ru ctures . Although there are hundreds of differen t species, they have only three general forms,which have been aptly compared to bi l l iard bal l s

,

lead penci l s, and corkscrews. Spheres,rods

,and

spi rals represent al l shapes . The spheres may belarge or smal l

,and may group themselves in va

rio us ways ; the rods may be long or sho rt, thicko r slender ; the spi rals may be loose ly or tight lycoi led

,and may have on ly o ne or two or may

have many coi l s,and they may be flex ible or

stiff but sti ll rods,spheres

,and spirals comprise

al l types (Fig . I ) .I n size there i s some variation

,though not

very great . Al l are extremely minu te,and never

visibl e to the naked eye . The spheres vary from

p to I‘ to inches) . T he

rods may be no more than p. i n d iameter,or may be as wide as p to p, and i n leng th

2

1 8 T HE ST ORY OF G ERM L IFE.

vary al l the way from a length scarcely longerthan thei r diameter to long threads. About the

same may be said of the spiral forms. They are decidedly the smal lest l iving o r

gan isms which ou r microscopes have revealed .

I n t hei r method of growthwe find one of the most C haracteristic featu res Theyun iversal ly have the powero f mul tip l ication by simpledivision or fi ssion . Each indi vidual elongates and thendivides in the middle into

Fm. I ._Genm1 shapes

two simi lar halves,each of

o f bacteria ; a, spheri wh ich then repeats the proc

il fo r

?“13,R8

04 cess . This met hod of mul

ida

g’

jfms?“ 9"

tiplicatio n by simple di visioni s the distinguishing. mark

which separates the bacteria from the yeasts,the

latter p lants mu ltiplying by a process known asbudding. Fig . 2 shows these two methods ofmu ltipl ication .

Whi le al l bacteria thus mu ltiply by divi sion,

certain di ff erences in the detai l s produce ratherStriking differences in the resu lts. Consideringfi rs t the spherical fo rms

,we find that some species

divide,as described , i n to two, which separate at

once,and each of which in tu rn divides in the o p

po site di rection , cal ledM z'

cro coccus, (Fig . Other

species div ide on ly in one di rection . Frequentlythey do no t separate after div iding

,but remain

attached . Each , however, again elongates anddivides again

,but al l sti l l remain attached . There

are thu s formed long C hain s o f spheres l ike strings

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20 T HE ST ORY O F G ERM L IFE.

tococcus,and al l wh ich divide i n th ree division

planes fo rm another genu s, Sarcz'

rza,etc.

FIG . 6. Separate ro dssho wing variatio ns in

FIG . 5 .—Sa.rcina. size , magn ified abo ut

1 000 diameters.

The rod - shaped bacteria also differ somewhat,

but to a less extent. They almost always dividei n a p lane at right angles to their longest dimension . But here again we find some species separating immediate ly after di vision

,and thus always

appearing as short rods (Fig. whi le othersremain attachedafter div i sionand form longC hains. Sometimes they appear to contin ueto increase i nlength withou tShowing anysigns of divi s

FIG . 7.—Rod- fo rms united to fo rmChains. i0 11

, and in thi sway lo ngthreads

are formed (Fig . These threads are,however

,

poten tial ly at least, long C hains o f short rods,and

under proper conditions they wi l l break up in tosuch short rods

,as shown i n Fig. 7 a . Occasion

al ly a rod species may divide lengthwise,but th is

i s rare. Exactly the same may be said of the

BAC T ERIA AS PLANT S.

spi ral forms . Here,too

,we find sho rt rods and

long C hains, or long spi ra l fi laments in which canbe seen no divisioni nto shorte r elements,bu t which

,under cer

tain conditions,break

up in to short section s

(Fig .

RAPIDIT Y O F

MU L'

T IPL IC AT IO N .

I t i s thi s power o fmu ltipl ication by div i sion that makes bacteria agents of suchsign ificance . Thei rminute si z e wou ldmake them harmlessenough i f i t were notfo r an extraordinarypower of mu ltip l icat ion . This power ofgrowth and divi sionis almost incredibl e .

Some O f the SpeciesFIO . 8 .

—Vario us types o f spiralWt I’l have been care bacteria .

fu l ly watched underthe microscope have been found under favou rableconditions to grow so rapidly as to di vide everyhalf hou r

,o r even less. The number of o ffspring

that wou ld resu l t in the cou rse of twenty - fo u rhou rs at thi s rat e is of course easi ly computed .

In one day each bacteri umwou ld produce overdescendants

,and in two days abou t

I t has been further calcu lated

2 2 T HE ST ORY OF GERM L IFE .

that these wou ld form about aso l id pin t of bacteria and weigh abou t a pound .

At the end of the thi rd day the total descendan tswou ld amount to and wou ldweigh about pounds. O f cou rse thesenumbers have no significance

,for they are never

actual or even possible numbers . Long beforethe offspri ng reach even in to the mi l l ion s thei rrate of mu ltipl ication i s C hecked ei ther by lack offood or by the accumu lation of thei r own excreted products, which are inj urious to them . Butthe figu res do have in terest since they show fain tly wha t an unl imi ted power of mu ltip l ication theseo rgan isms have, and thus show u s that in dealingwith bacteria we are deal ing with forces of al

most infin ite ex ten t.Thi s wonderfu l power o f growth is ch iefly due

to the fact that bacteri a feed upon food which i sh ighly organi zed and already in condition for abso rption . Most plants must manufactu re thei rown foods out of S impler substances

,l ike carbon i c

diox ide (C 02) and water, but bacteria , as a ru le,feed upon co mplex o rgan ic material al ready prepared by the prev io u s l i fe of plants o r animals.For this reason they can grow faster than otherplants . Not being obliged to make thei r ownfoods l ike most plants

,nor to search for i t l ike

an imals,bu t l i ving in its midst

,thei r rapidi ty of

growth and mu ltip li cation i s l imited on ly by theirpower to sei ze and assimi late th i s food . As theygrow in such masses o f food

,they cause certai n

C hemical changes to take place i n i t , changesdoubt less di rectly connected with thei r u se of thematerial as food . Recogn ising that they docause C hemical changes in food material , and t e

membering this marvel lous power of growth , we

BAC T ERIA AS PL ANT S.

are prepared to bel ieve them capable of produ cingC hanges wherever they get a foothold and begint o grow . Thei r power of feeding upon complex organic foodand producing C hemical C hanges therein ,together wi th thei rmarvel lou s power ofassimi lating thi s material as food, makethem agents i n Nature of extreme im FIG . 9.

—Showing vario us shapedportance .

“fis

DIFFERENC ES BETWEEN D IFFERENT SPEC IES O F

BAC T ERIA .

Whi le bacteria are thus very simple in fo rm,

there are a fewother sl ight variat ions i n detai lwhich assi st i n di st inguishing them .

The rods are sometimes very blunt -at

t he ends,almost

as i f o ut squareacross

,whi le in

o ther species theyare more roundedand occasional l y

FIG . Io .—Bacteria surro unded by cap

Sh-

ghtl'v tapering

sules : a and b represent zo Oglcea ; (Flg Somec, C hains

o

o f co cci w ith a capsule ; tImes they are sur

gtmsss: zine

sPM rounded by a thm

and y the pro to plasm.layer O f somegelat


in o us substance,which forms what i s called a

capsule (Fig . This capsu le may connect themand serve as a cement

,to prevent the separate

e lements of a chain from fal l ing apart (Fig. 1 0 c) .Sometimes sucha gelatinou s secretion wi l l un i tegreat masses ofbacteria intocl usters

,which

may float on thesu rface of thel iq uid in whichthey grow ormay sink to thebottom . Suchmasses are cal ledz o oglcea,

and thei rgeneral appearan ce serves asone of the characters for distin

guishing di fferen t species o f

FIG . I I .—Vario us types o f bacteria “co lo bacteria (Fig 1 0

,

nies fo rmed when gro wing in nutrien t a and b) , Whenelatine . Each differen t type o f co lo ny

Igs pro duced by a differen t species o f growmg m Sohdbacterium. medIa, such as a

n u tr itiou s l iquidmade sti ff wi th gelatin e

,the di fferen t species have

d i fferent methods of spreading from their centralpoint o f o rigi n . A single bacteri um in the midsto f such a sti ffened mass wi l l feed u pon i t and produce descendants rapid ly ; but these descendants,not being able to move through the gelatin e

,wi l l

remain C l u stered together in a mass,which the

BAC TERIA AS PL ANT S. 25

bacterio logist cal ls a co lo ny . But thei r method ofC l ustering, due to different methods of growth , i sby no means a lways a l ike

,and these colon ies

show great di fferences i n general appearance .

The di fferen ces appear to be constan t, however,for the same species o f bacteria, and hence theshape and appearance of the co lony enable bacterio lo gists to d iscern di ff eren t species (Fig .

All these po ints of di fference are of practical u seto the bacteriologist in distingui sh ing species .

SPORE FORMAT ION .

In additio n to thei r power of reproduction bysimple d iv ision , many species o f bacteria have asecond method by means o f spo res. Spores arespecial ro unded or oval bi ts of bacteria protoplasmcapable of resi sting adverse condit ions whichwou ld destroy the ordinary bacteria . They ari seamong bacteria in two di fferent methods .

E ndogeno us sperm—These spores ari se i nsideo f the rods or the spiral forms (Fig. Theyfirst appear as sl ight granu lar masses

,or as dark

points which become gradual ly d istinct from therest o f the rod . Eventual ly there is thus formedinside the rod a clear

,high ly refracti ve

,spherical

o r oval spore,which may even be of a greater

diameter than the rod producing it,thu s cau sing

i t to swel l o ut and become spind le formed (Fig.

1 2 c) . These spores may fo rm in the middle or atthe ends of the rods (Fig . They may use upa l l the pro toplasm of the rod i n thei r formation

,

o r they may use on ly a smal l par t o f i t,the rod

which fo rms them contin u ing i ts acti vi ties i n spi teo f the formation of the spores wi thin it . They arealways clear and high ly refractive from contain


ing l i t t le water, and they do not so readi ly absorbstain ing material as the ordinary rods. They appear to be covered with a layer o f some substancewhich resists the stain

,and which also enables

them to resi st vario us external agencies. This protect

0 i ve covering,to

gether wi th thei rsmal l amoun t o fwater

,enab l es them

to resist almost anyamoun t of drying

,

a high degree ofheat

,and many

other adverse condit io ns. Commonly the spores breakou t of the rod

,and

the rod producingthem dies

,al though

sometimes the rodmay con t i n ue its

FIG . 1 2 .—Endogeno us spo res : a and activi ty even after

h, Spo res fo rming at in tervals inthe spores have

the rods ; c, Spo res fo rming in themiddle o f the ro ds and causing the been produced .

middle to swell d, Spo res fo rming at the end

’

o t the ro ds andA r

filz r og eflmf ‘g

causing the end to swell. 5PM“ —C ertalnspecies of bacteri a

do n o t produce spores as j u st described,bu t

may give rise to bodies that are sometimes cal ledarthro spo res. These bodies are formed as shortsegments of rods (Fig . 1 3 a ) . A long rod maysometimes break Up i n to several short roundedelements

,which are clear and appear to have a

somewhat increased power of r esist ing adverse

28 T HE ST ORY OF G ERM L IFE.

of the poin ts for distingu ishing species . Somespecies do no t form spores

,at least under any of

the condi tions in which they have been studied .

Others form them readi ly in almost any condition,

and others again on ly under special condition swhich are adverse to theirl i fe . The method of sporefo rmation i s always uniform for any single species .

Whatever be the methodof the formation of the

spore , i ts pu rpose in the

l i fe o f the bacteri um is always the same . I t servesas a means of keeping the

species al ive under condition s o f adversi ty . I tspower of resist ing heat ordry ing enables i t to l ivewhere the o rdinary active

FIG . I4o-

7F0rmatio n o f forms wou ld be speedi ly

igzs

o

’

tgrflggf ual“ms ki l led . Some of these

spores are capable of re

sisting a heat o f 1 80° C . (3 60° F . ) for a short time ,

and boi l i ng water they can resist for a long time .

Such spores when subsequently p laced u nder tav o urab le condit ions wi l l germinate and start bacterial activ i ty anew.

MO T IO N .

Some species o f bacteria have the power ofactive motion

,and may be seen darting rapid ly

to and fro in the l iquid in which they are growing. This motion i s produced by flagella whichprotrude from the body . These flagel la (Fig . 1 5 )

BAC T ERIA AS PLANT S. 29

arise from a membrane surrounding the bacterium,

bu t have an in timate connection wi th the proto

FIG . 1 5 .—Bacteria pro vided w ith flagella : a, Single flagellum; b ,

T w o flagella ; C , A tuft o f flagella at o ne end ; d,T ufts o f

flagella at bo th ends ; e , Un ifo rm co vering o f flagella ; f,Sho wing the o rigin o f flagella fromthe o uter lay er o f the body .

plasmic content . Thei r distribution i s d ifferen tin di fferen t species o f bacteria. Some species


have a single flagel l um at one end ig. 1 5 a) .Others have one at each end (Fig. 1 5 Others

,

again , have, at least j u st before dividing, a bunchat one o r both ends (Fig . 1 5 c and whi le o thers

,

again,have many flagel la distributed al l over the

body in dense pro fu sion (Fig. 1 5 e) . These flagel lakeep up a lashing to and fro i n the l iqu id

,and the

lash ing serves to prope l the bacteria t hrough theliqu id.

INT ERNAL ST RU C T URE.

I t i s hardly possible to say much abou t thestructure of the bacteria beyond the descript io no f thei r ex ternal fo rms . With al l the variations

in detai l mentioned,they are

extraordinari ly simple, andabout al l that can be seen i sthei r external shape . Ofcourse

,they have some in

ternal structu re,bu t we

know very l it t le in regard toi t . Some microscopists havedescribed certain appearan

ces which they thin k indicate in ternal structu re . Fig.

1 6 shows some of these ap

pearances. The mat ter i s asyet very obscure, however .The bacteria appea r to have

FIG 16 —In ternal Sun”a membranous

.

co vering

my, o f bacteria.

wh ich somet imes 15 of a cellulo se nature . Within it i s

protoplasm which Shows vario us uncertain ap

pearances. Some microscopists have thoughtthey could find a n ucleus, and have regardedbacteria as ce l ls wi th inclosed nucleii (Figs . 1 0 c

BAC T ERIA As PL ANT S. 3 1

and 1 5 f) . Others have regarded the whole bacterium as a n ucleu s without any protoplasm

,

whi le others,again

,have concluded that the di s

cerned internal structu re is nothing except an ap

pearance presented by the physical arrangement ofthe protop lasm . Whi le we may bel ieve that theyhave some internal structure

,we must recognise

that as yet microscopists have not been able tomake i t ou t . III short

,the bacteri a after two

cen tu ries of study appear to us about as they didat first . They must st i l l be described as min utespheres

,rods

,or spi rals

,with no fu rther discern

ible structure,sometimes mo ti le and sometimes

stationary,sometimes producing spores and some

times not,and mult iplying u niversal ly by binary

fi ssion . With al l the development of the modernmicroscope we can hardly say more than this.O ur advance in know ledge of bacteria is connectedalmost who l ly with their methods of growthand the effects they produce in Nature .

ANIMAL S OR PL ANT S ?

There has been in the past no t a l i tt le question as to whether bacter ia shou ld be rightlyclassed with plants or wi th an imals . They cerf ain ly have characters which al ly them with both .

Thei r very common power of active i ndependentmotion and their common habi t of l ivi ng uponcomplex bodies fo r foods are animal C haracters

,

and have lent force to the suggestion that theyare true animals . But their general form

,their

method of growth and formation of threads,and

thei r method of spore formation are qu ite plantl ike . Their general form i s very simi lar to agro up of low green plants known as Oscillarz

'

a .


Fig. 1 7 shows a group o f these O scillariae , andthe simi lar ity o f thi s to some of the thread - l ike

bacteria i s decided . The 0scz

'

llarz'

ce are,how

ever,tru e plants

,

and are of a

green colou r .Bacteria aretherefore to - daylooked upon asa low type o fplant which hasno ch lorophyl l

,

but i s related toO sct

'

llarice. Theabsence of theC h lorophyl l hasforced them t o

adopt new relations to food

,

and compel sFIG . 1 7.

—T hreads o f Osci'Ilari'a , the nearest them to feedallies o f bacteria.

upon complexfoods instead of the simple on es

,which form the

food of green plan ts . We may have no hesitat ion

,then

,i n cal l ing them plan ts . I t i s i nterest

ing to notice that with this idea their place in theo rgan ic world i s reduced to a smal l one sy stematically . They do not form a class by themselves,but are simply a subclass, or even a fami ly, anda fami ly C losely related to several other commonplants . But the absence of chlorophyl l and theresu lting pecu l iar l i fe has brought abou t a cu ri

C hlo rophyll is the green co lo uringmatter o f plan ts.

BAC T ERIA As PLANT S. 3 3

o us anomaly . Whereas thei r C losest al l ies areknown on ly to botan ists, and are of no i nteresto utside of their systemati c relations, the bacteriaare fami l iar to every one, and are demanding thel i fe attention of hundreds of investigators. I t i stheir absence of chlo rophyl l and thei r con sequen tdependence upon complex foods which has produced thi s anomaly .

C L ASSIFIC AT IO N O F BAC T ERIA .

While i t has general ly been recogni sed thatbacteria are p lan ts

,any furthe r classification has

proved a matter of great di fficu l ty, and bacterio logists find i t ex tremely di fficu l t to devise means ofdi stingu ishing species . Thei r ex treme simpl ici tymakes i t no easy matter to find points by whichany species can be recogn ised . Bu t in spite o ftheir simi lari ty

,there i s no doubt that many

di ff eren t species ex ist . Bacteria which appear tobe almost identical

,under the microscope prove

to have enti rely different properties,and must

therefore be regarded as distinct species . Bu thow to di sti nguish them has been a puzz le .

Microscopi sts have come to look upon the di ffere nces i n shape

,mult ip l ication

,and formation of

spores as furn ish ing data su fficient to enablethem to divide the bacteria i n to genera . Thegenu s B acillus

, fo r instance, i s the name given toa l l rod - shaped bacteria which form endogenousspores

,etc. But to distingu i sh smal ler subdi

visions it has been found necessary to fal l backupon other characters

,such as the shape of the

co lony produced i n sol id gelatine,the power to

produce disease,o r to oxidize n i tri tes, etc . Thus

at presen t the di fferent species are distinguished

3


rather by their physiological than thei r morphological characters . This i s an unsati sfacto rybasis o f classification , and has produced muchconfusio n i n the attempts to classi fy bacteria .

The problem of determin ing the speci es of bacteria i s to - day a very difficu lt one

,and wi th

our best methods i s sti l l unsati sfactori ly solved .

A few species of marked character are wel lknown

,and thei r powers o f action so wel l under

stood that they can be readi ly recognised ; buto f the great host o f bacteria studied

,the large

majori ty have been so sl ightly experimented uponthat their characters are not known

,and i t i s im

possible, therefore, to di stingu ish many of themapart . We find that each bacterio logist workingin any special l ine commonly keeps a l i st of thebacteria which he finds

,with su ch data i n re

gard to them as he has coll ected . Such a l ist i so f val u e to him

,but commonly of l i tt le value to

o ther bacterio logists from the insu fficiency of thedata . Thu s i t happens that a large part o f thedi fferen t species o f bacteria described i n l i teratu reto - day have been found and studied by one investigat o r alone . By him they have been described and perhaps named . Qu ite l i kely the

same species may have been found by two orthree o ther bacterio logists

,bu t owing to the

difliculty of comparing resu l ts and the incomple teness of the descriptions the iden ti ty o f thespecies i s no t discovered

,and they are probably

described again under different names. T he

same process may be repeated over and ove ragain

,unti l the same species o f bacteri um wi l l

come to be known by several di fferen t names,as

i t has been studied by different observers.


thi rd period it i s a simple mass of sphericalspo res. A spherical form

,when i t lengthens

before dividing,appears as a Short rod

,and a

short rod form after div iding may be so short asto appear l ike a spherical organism .

With al l these reasons for con fu sion,i t is no t

to be wondered at that no sati sfactory Classificat ion of bacteria has been reached

,or that differ

en t bacterio logi sts do not agree as to what constitutes a species

,or whether two forms are iden t ica l

or not . But with al l the con fu sion there i s slowlybeing obtained something l ike system . I n spi teof the fact that species may v ary and showdifferent properties u nder differen t condi tion s

,

the fundamental constancy of species i s everywhere recogni sed to - day as a fact . The membersof the same species may show di fferen t propertiesu nder different condi tions

,bu t i t i s bel ieved that

u nder identical conditions the properties wi l l beconstant . I t i s no more possible to con vert onespecies in to another than i t i s among the highero rders of p lan ts. I t i s bel ieved that bacteriado form a group of plants by themselves

,and

are not to be regarded as stages in the historyo f higher plan ts . It i s bel ieved that . togetherwi th a considerable amount o f variabi li ty and

an occasion al somewhat long l ife hi story withsuccessive stages

,there i s al so an essential con

stancy .

‘A systematic C lassification has beenmade which i s becoming more or less satisfacto ry .

We are constantly learning more and more of theC haracters

,so that they can be recognised i n

different p laces by di fferen t observers . I t i s theconv iction of al l who work with bacteria that

,in

spi te of the difficu lt ies,i t i s on ly a matter o f t ime

when we shal l have a classification and descrip

BAC T ERIA AS PLANT S.

t ion o f bacteria so complete as to characterizethe di ff erent species accu rately .

Even wi th o ur present i ncomplete knowledgeof what characteri zes a species

,i t i s necessary to

u se some names . Bacteria are common ly given ageneric name based upon thei r m icroscopic ap

pearance . There are on ly a few of these names.M z

'

croco ccus,S treptoco ccus, S taphy lo co ccus, Sarcz

'

na ,

Bacterium,Bacillus

,Spirillum

,are al l the names in

common use applying to the ordinary bacteria .

There are a few others less commonly used . T o

thi s generic name a specific name is commonlyadded

,based upon some physio logical character.

For example,B acillus typho sus i s the name given

to the baci l l u s which causes typhoid fever. Suchnames are of great use when the species i s a common and wel l - known one

,but of doubtfu l value

for less - known species . I t frequently happensthat a bacteriologist makes a study of the baCteria found in a certain local i ty

,and obtains thus

a long l ist of species hi therto unknown . I n thesecases i t i s common simply to number these species rather than name them . This method is frequent ly advi sable , since the bacterio logi st canseldom hunt up al l bacterio logical l i teratu re wi thsufficient accuracy to determine whether someother bacterio logist may not have found thesame species in an enti rely di fferent local i ty .

O ne bacteriologist,for example

,finds some sev

en ty di fferen t species of bacteria i n di fferentcheeses . He studies them enough for his o wn

purposes,but not su fficient ly to determine whether

some other person may not have found the samespecies perhaps in mi lk o r water . He therefore simply numbers them—a method which conveys nosuggestion as to whether they may be new species


or not . This method avo ids the giving of separatenames to the same species fo und by di fferen tobservers

,and i t is hoped that gradual ly accumu

l ating knowledge wi l l in time group together theforms wh ich are real ly identical

,bu t which have

been described by different observers .

WHERE BAC T ERIA ARE FO UND .

There are no other plants or an imals 80 univ ersally fo und i n Nature as the bacteria . I t i sthi s universal presence

,together with thei r great

powers o f mu ltipl ication,which renders them of

so much importance in Natu re. They ex ist almosteverywhere o n the su rface of the earth . Theyare in the soi l

,especial ly at i ts su rface . They do

no t ex tend to very great depths of soi l,however

,

few ex isting below fou r feet of soi l . At the surface they are very abundant

,especial ly i f the soi l

i s moist and fu l l of organ ic material . The number may range from a few hundred to one hundred mi l l ions per gramme .

! The soi l bacteriav ary also in species

,some twosco re differen t spe

cies having been described as common in soi l .They are in al l bodies of water

,both at the

su rface and below i t . They are found at considerab le depths in the ocean . Al l bodies of freshwater con tain them

,and al l sediments in such

bodies o f water are fi l led with bacteria . Theyare in streams of runn ing water in even greaterquanti ty than in standing water. This i s simplybecau se ru nning streams are being constan tlysupplied with water which has been wash ing thesu rface of the count ry and thus carrying o ff a l l

O ne gramme is fifteen grains.

BAC T ERIA AS PLANT S . 3 9

su rface accumulation s . Lakes or reservoi rs, however

,by standing qu iet al low the bacteria to set

t l e to the bottom,and the water thus gets some

what purified . They are i n the ai r,especial ly i n

region s of habitation . Thei r numbers are greatest near the su rface of the gro und

,and decrease

i n the upper strata o f ai r . Anything whichtends to raise dust increases the n umber of bacteria i n the air greatly

,and the du st and emana

tions from the C lothes o f people crowded in aclose room fill the ai r wi th bacteria in very greatnumbers . They are found in excessi ve abundance in every bit of decaying matter wherever i tmay be . Manure heaps, dead bodies of animals,decaying trees

,fi l th and slime and muck every

where are fi l led wi th them,for i t i s in such p laces

that they find thei r best nouri shment. The bodies o f animals contai n them in the mou th

,stom

ach,and in testine in great numbers

,and thi s i s

,o f

course,equal ly true of man . On the surface o f

the body they C l i ng i n great quanti ty ; attachedto the clothes, u nder the finger nai l s, among thehai rs

,in every possib l e crevice o r h iding place in

the skin,and i n al l secretions . They do not

,

however,occur i n the tissues o f a heal thy indi

vidu al,either in the blood

,muscle

,gland

,or any

other o rgan . Secretions,such as mi lk , u rine, etc . ,

always contain them,however

,since the bacteria

do exist i n the ducts of the glands which conductthe secret ions to the ex terior

,and thus

,whi le the

bacteria are never i n the heal thy gland i tse l f,

they always succeed in contaminating the secretion as i t passes to the exterio r. Not only higheranimals

,bu t the lower an imals also have thei r bod

ies more or less covered wi th bacteria . Flies havethem on thei r feet

,bees among thei r hai rs

,etc .

0 THE ST ORY OF G ERM L IFE.

I n short,wherever on the face of Natu re there

i s a lodging place for dust there wi l l be foundbacteria . I n most of these local i ties they aredormant, or at least growing on ly a l i tt le . Thebacteria cl inging to the dry hai r can grow bu t l i tt l e

,i f at al l

,and those in pure water mul tip ly very

l i ttl e . When dried as dust they are en ti rely dormant . But each indiv idual bacterium or sporehas the poten tia l power o f mu l tiplicat ion al readyn oticed , and as soon as i t by acciden t fal l s upona place where there i s food and mo istu re i t wi l lbegin to mu l ti ply . Everywhere i n Natu re

,then

,

ex ists thi s group of organ i sms with i ts almo st inconceivable power of mu ltipl ication

,bu t a power

held in check by lack of food . Furnish themwith food and thei r potentia l powers becomeactual . Such food is provided by the dead bodies of animal s or plants, or by animal secretions,or from vario u s other sources . The bacteria whichare fortunate enough to get furn ished with suchfood material continue to feed upon i t un ti l thefood supply is exhausted or thei r growth i sC hecked in some other way. They may be re

garded,therefore

,as a con stant and un iversa l

power usual l y held in C heck . With thei r universal presence and thei r powers of producing ,

chemical changes i n food materia l,they are ever

ready to produce changes i n the face of Nature,

and to these changes we wi l l now turn .

USE OF BAC T ERIA IN T HE ART S. 4 1

CHAPTER II .

MISC EL L ANEO US USE O F BAC T ERIA IN T HE ART S .

T HE foods upon which bacteria l i ve are inendless variety , almost every product of animalo r vegetable l ife serving to supply thei r needs .

Some species appear to requi re somewhat defini tek inds of food

,and have therefore rather narrow

condi tions of l i fe,but the majori ty may l i ve upon

a great variety o f organ ic compo unds. As theyconsume the materia l which serves them as foodthey produce chemical C hanges therein . TheseC hanges are largely o f a natu re that the C hemistknows as decomposition changes . By this i smean t that the bacteria

,seiz ing ho ld o f ingre

dich ts which consti tu te thei r food,break them to

pieces chemical ly . The molecu l e o f the originalfood matter is spli t in to simpler mo lecu les

,and

the food i s thus changed in i ts C hemical nature .

AS a resu l t,the compounds which appear in the

decomposin g solu tion are common ly Simpler thanthe original food molecu les . Such products arein general cal led decompo sitio n products

,or some

times cleavageproducts. Sometimes,however

,the

bacteria have,in addition t o thei r power of pu l l

i ng thei r food to pieces,a fu rther power o f bui ld

ing other compounds o ut of the fragmen ts, thu sbui lding up as wel l as pu l l ing down . But

,how

ever they do it,bacteria when growing in any

food material have the power of giving rise ton umerou s products which did no t ex i st in thefood mass before . Because o f thei r ex trao rdi

nary powers o f reproductio n they are capable ofproducing these C hanges very rapid ly and can

42 T HE ST ORY OF G ERM L IFE .

give ri se in a short time to large amounts o f thepecu l iar products o f thei r growth .

I t i s to these powers of producing chemicalchanges i n thei r food that bacteria owe al l thei rimportance in the world . Thei r power o f Chemically dest roying the food products is in i tsel f o fno li tt l e importance

,but the products which arise

as the resu l t o f thi s series of chemical C hangesare of an importance in the world which we areon ly j ust beginning to appreciate . I n ou r at

tempt to ou tl ine the agency which bacteria p layin our indu stries and in natu ral processes as wel l

,

we shal l notice that they are sometimes o f val u esimp ly for thei r power of producing decomposit ion ; but thei r greatest value lies i n the fact thatthey are impo rtant agen ts becau se of the products of thei r l ife .

We may notice,i n the fi rst p lace , that in the

arts there are several industries which may properly be classed together as maceratio n industries,al l o f which are based upon the decomposi tionpowers of bacteria . Hard ly any an imal o r vegetable su bstance is able to resi st their soften ingi nfluence

,and the artisan rel ies u pon thi s power

i n severa l d i fferen t di rection s .

BENEFIT S DERIVED FROM POWERS O F

DEC OMPO S IT IO N .

L inen .

— Linen consi sts of certain woody fibreso f the stem of the flax . The flax stem is notmade up enti rely of the val uable fibres, butlargely of more bri tt le wood fibres

,which are of

no u se . The valuable fibres are,however

,close

ly u nited with the wood and with each other i nsu ch an in timate fash ion that i t i s impossible to

44 T HE STORY OF GERM L IFE.

has not been scien tifical ly studied unti l very t e

cen t ly . The baci l l us which produces the “rett ing is known now

,however

,and i t has been

shown that the retting is a process o f decomposi tion of the pectin cement . No method ofseparating the l inen fibres i n ° the flax from thewood fibres has yet been devised which dispenseswith the aid o f bacteria .

j ute andH emp—Almost exactly the same usei s made of bacterial action i n the manu facture ofj ute and hemp . The commercial aspect of thej ute indu stry has grown to be a large one

,inv o lv

ing many mi l l ion s o f dol lars . Like l inen,j u te i s

a fibre of the inner bark of a p lant,and is mixed

i n the bark with a mass of other u seless fibrousmaterial . As in the case of l i nen

,a fermenta

t ion by bacteria i s depended upon as a means o fsoftening the material so that the fibres can bedisassociated . T he process i s cal led “retting,

”

as i n the l inen manufacture . The detai l s of theprocess are somewhat different . The j ute i s commou ly fermen ted in tanks o f stagnant water

,al

though sometimes it i s al lowed to soak i n riverwater for a su fficien t length of time to producethe soften ing. After the fermentation is thu sStarted the j u te fibre i s separated from the wood

,

a nd i s of a su fficient flexibi li ty and toughness tobe woven into sacking

,carpets

,cu r tains

,table

covers,and other coarse cloth .

Practical ly the same method is used in separating the tough fibres o f the lzemp. The hempplant contains some long flexible fibres wi th otherso f no value

,and bacterial fermentatio n i s rel ied

upon to soften the tissues so that they may beseparated .

C ocoanut fibre, a somewhat simi lar material, is

USE OF BAC T ERIA IN T HE ART S. 45

O btained from the husk of the cocoanu t by thesame means. The unripened husk i s al lowed tosteep and fermen t i n water fo r a long time

,si x

months o r a year being requ i red . By this timethe husk has become so softened that i t can bebeaten unti l the fibres separate and can be removed . They are subsequent ly made in to a number of coarse articles

,especial ly val u able for thei r

toughness . Door mats,brushes

,ships ’ fenders

,

etc .

,are i l l ustrations of the so rt of articles made

from them .

In each of these processes the fermentationmust have a tendency to soften the desi red fibresas wel l as the connecting substance . Putre fac

tion attacks all kinds of vegetable tissue, and ifthi s “retting ” conti n ues too long the desi redfibre is decidedly inj ured by the softening effectof the fermentation . I t i s qui te probable that

,

even as common ly carried on,the fe rmentation

has some - sl igh t i n j u riou s e ffect u pon the fibre,

and that i f some purely mechan i cal mean s cou ldbe devised for separati ng the fibre from the woodi t wou ld produce a better materia l . But suchmechan ica l means has not been devised

,and at

present a pu trefactive fermentation appears tobe the on ly practical method of separat ing thefibres .

Spo nges— A somewhat simi lar u se i s madeof bacteria i n the commercial preparation ofsponges . The sponge of commerce i s simplythe fibrou s skeleton of a marine an imal . Wheni t i s al ive thi s ske leton is completely fi l led wi ththe softer parts of the animal

,and to fit the

sponge fo r u se thi s so fter o rganic material mustbe go t rid of. I t i s easi ly accompl i shed by rott ing. The fresh sponges are al lowed t o stand in


the warm sun and very rapid ly decay . Bacteriamake their way into the sponge and thorough lydecompose the soft tissues . After a short pu trefaction of thi s so rt the softened o rganic mattercan be easi ly washed o u t of the ske leton and

leave the clean fibre ready fo r market .L eather preparatio n .

— T he tan n ing of leatheri s a purely chemical p rocess

,and in some pro

cesses the who le operat ion of preparing theleather is a C hemical one . In o thers

,however

,

especial ly i n America,bacteria are brought in to

action at one stage . The dried hide which comesto the tannery must first have the hai r removedtogether wi th the o u ter skin . The hide fo r thi spurpose mu st be moisten ed and softened . In

some tanneries thi s i s done by steeping i t inC hemicals . In others

,however

,i t i s pu t in to

water and S l igh tly heated u n ti l fermentationari ses . The fermentation so ftens i t so that theou ter skin can be easi ly removed with a kni fe

,

and the removal o f hai r i s accompl ished at thesame time . Bacteria l pu trefaction in the tanneryi s th u s an assi stance i n preparing the Skin forthe tann ing proper. Even i n the subsequenttanning a bacterial fermentation appears toplay a part

,but l i ttl e i s yet known i n regard

to it .

Ill aceratio n of skeleto ns—The maki ng of skeletons fo r mu seums and anatomica l instruction ingeneral i s no very great i ndustry, and yet i t i sone o f importance . In the mak ing of skeletonsthe process of maceration i s common ly u sed asan aid . The maceration consi sts simply in al lowing the skeleto n to soak in water fo r a day ortwo after clean ing away the bu lk of the muscles.The putrefaction that arises soften s the connect


ive t issues so much that the bones may be readi lyC leaned o f flesh .

C itric acid—Bacter ial fermentation is employed al so i n the ordinary preparation o f ci tricacid . The acid i s made ch iefly from the j u ice ofthe lemon . The j uice i s pressed from the fru i tand then al lowed to ferment . The fermentationaids in separating a muci laginou s mass and making it thus possible to obtain the C i tric acid in apurer condi tion . The actio n is probably simi larto the maceration processes described above

,al

though it has not as yet been studied by bacterio logists.

BENEFIT S DERIVED FROM T HE PRODUC T S O F

BAC T ERIA L L IFE .

While bacteria thus play a part in o ur indu st ries simply from thei r power o f produci ng decomposi tion

,it i s primari ly because o f the prod

n o ts o f thei r action that they are of val ue.

Wherever bacteria seize hold of o rgan ic matterand feed upon i t

,there are certain to be devel

O ped new chemical compounds,resu l ting largely

from decomposition,but part ly also from con

structive processes . These new compounds areof great variety . Diff eren t species o f bacteriado no t by any means produce the same compounds even when growing in and decomposingthe same food material . Moreover

,the same

species of bacteria may give ri se to di fferen tproducts when growing in di fferen t food material s . Some of the compounds produced by suchprocesses are po i sonou s

,others are harmless .

Some are gaseous,o thers are l iqu ids . Some

have pecu l iar odou rs,as may be recogn ised from


the smel l ari sing from a bi t of decaying meat .Others have pecu l iar tastes

,as may be real i zed

in the gamy taste o f meat which is in the incipient stages o f pu trefaction . By purely empirica lmeans mankind has learned methods of enco uragi ng the development of some of these products

,and

i s to - day making practi cal use of th is power,pos

sessed by bacteria,of fu rn ishing desi red C hemical

compounds . I ndustries invo lving the in vestmen tof hundreds of mi l l i on s of dol lars are foundedupon the products of bacterial l ife

,and they have

a far more important relation to ou r everydayl ife than i s common ly imagined . In many casesthe arti san who is dependent upon thi s action ofmicroscopic l i fe i s unaware of the fact . Hisprocesses are those which experience has taughtproduce desi red resu l ts

,but

,nevertheless

,hi s

dependence upon bacteria i s none the less fundamental .

BAC T ERIA IN T HE FERMENT AT IVE INDUST RIES.

We may notice , first, several miscel laneou s instances o f the applica t ion o f bacteria to variou sfermentative i ndustries where thei r aid is of moreor less val ue to man . I n some of the examplesto be mentioned the infl uence of bacteria i s profound and fundamental

,whi le in others i t i s on ly

incidental . The fermen tati ve indu stries of civ i l iz atio n are gigantic i n ex ten t

,and have come to

be an importan t facto r in modern civ i lized life .

The large part of the fermentation is based uponthe growth of a class of microscopic p lan ts whichwe cal l y easts. Bacteria and yeasts are bothmicroscopic plants

,and perhaps somewhat close

ly re lated to each other. T he botan ist finds a


difference between them ,based upon thei r method

of mul tip l i cation , and therefore places them i ndi fferen t classes (Fig . 2 , page In the ir general power o f producing chemical changes in thei rfood products

,yeasts agree close ly with bact eria

,

though the kinds of chemical C hanges are di ffe rent . The whole of the great fe rmentati ve industries

,in which are invested hundreds of mi l l ions

of dol lars,i s based upon C hemica l decompositions

produced by microscopic p lan ts . In the greatpart of commercial fermentations alcoho l i s theproduct desi red

,and alcohol

,though i t i s some

times produced by bacteria,i s ih commercial

quanti t ies produced on ly by yeasts . Hence i t i sthat

,although the fermentation s produced by

bacteria are more common in Natu re than thoseproduced by yeasts and give rise to a much largernumber of decomposi tio n products

,sti l l thei r com

mercial aspect is decidedly less importan t thanthat of yeasts . Nevertheless

,bacteria are n o t

wi thou t their importance in the ordinary fermentative processes . Although they are of no importance as aids in the common fermen tati veprocesses

,they are no t i n frequently the cau se of

much trouble . In the fermentatio n of mal t toproduce beer, or grape j u ice to produce wine, iti s the desi re of the brewer and vintner to havethis fermentation produced by pu re yeasts

,nu

mixed with bacteria . If the yeast i s pu re thefermentation Is uni fo rm and successfu l . But thebrewer and vintner have long known that thefermentat ion i s frequently interfered with by i rregulari ties . The troubles which ari se have longbeen known , but the bacterio logist has final lyd iscovered thei r cause

,and i n general thei r rem

edy . The cause o f the chief tro ubles which ari se


i n the fermentation is the presence of contamin ati ng bacteria among the yeasts . These bacteria have been more o r less carefu l ly studied bybacteriologists

,and their effect upon the beer or

wine determined . Some of them produce acidand render the products so u r ; others . make thembitter ; others, again , produce a sl imy materia lwhich makes the wine o r beer “ropy . Somethi ng l i ke a score of bacteria species have beenfound l iable to occur in the fermenting material and destroy the value of the product of boththe wine maker and the beer brewer . The species of bacteria which infect and inj u re wine arediff eren t from those which Infect and in j u re beer .They are ever presen t as possibi l i t ies in the greatalcoho l ic fermentatio ns . They are dangers whichmust be guarded against . I n former years thetroubles from these so urces were much greaterthan they are at presen t . Since i t has been demo nstrated that the d ifferen t imperfectio n s i n thefermentative process are due to bacterial impu rit ies

,common ly i n ' the yeasts which are u sed to

produce the fermen tation,methods of avoiding

them are readi ly dev ised . To - day the vintnerhas ready command of processes for avoidingthe tro ubles which ari se from bacteria

,and the

brewer i s always provided with a microscope toShow him the presence or absence of the contaminating bacteria . Whi le

,then

,the alcohol ic

fermentations are not dependent upon bacteria,the proper management of these fermentation srequ i res a knowledge of their habits and C haracters.

There are certain other fermentative processesof more or less importance in thei r commercial as

pects, which are directly dependent upon bacte


gradual conversion of the alcoho l in to acetic acid .

At the close of the process practical ly al l of thealcohol has disappeared . Ordinari ly

,however

,

n o t al l o f i t has been converted into acetic acid,

fo r the ox idation does no t al l stop at thi s step.

As the oxidation goes on , some of the acid is

oxidized into carbon ic diox ide,whi ch 15

,of cou rse

,

di ssipated at once into the ai r,and i f the process

i s al lowed to continue unchecked fo r a longe nough period much of the acetic acid wi l l be losti n th is way .

The oxidation of the alcohol in al l commercial production of vinegar i s brought abou t bythe growth of bacteria in the l iqu id . When thev inegar production i s going on properly

,there is

formed on the top of the l iquid a den se fe l ted massknown as the “mother of vi negar . This massproves to be made of bacteria which have thepower of absorbing oxygen from the ai r

,or

,at al l

events,of causing the alcoho l to un ite w i th o xy

gen . I t was at fi rst thought that a single speciesof bacterium was thus the cause of the ox idationo f alcoho l

,and this was named Aly coderma aceti.

But fu rther study has shown that several havethe power

,and that even in the commercial man

ufacture of vinegar severa l species play a part

(Fig. although the di fferen t species are not yetvery thorough ly studied . Each appears to actbest under di fferen t conditions . Some of themact slowly

,and others rapidly ,

the slow - growingspecies appearing to produce the larger amoun tof acid i n the end . After the amount of aceticacid reaches a certai n percentage

,the bacteria are

unable to produce mo re,even though there be al

cohol sti l l le ft unoxidi zed . A percentage as highas fou rteen per cen t . commonly destroys al l thei r


power of growth . The production of the acid i swhol ly dependen t upon the growth of the bacteria,and the secret of the successfu l vinegar manufactu re is the ski l fu l manipu lation of these bac

ca n“FIG . 1 8 .

—Bacillus acetz'cum, the bacteriumwhich is the commo ncause o f the vinegar fermen tatio n .

teria so as to keep them in the pu rest conditionand to give them the best oppo rtuni ty for growth .

One method o f vinegar manufactu re which i squi te rapid i s carried on in a sl ightly di fferen tmanner . A tal l cyl indrical chamber i s fil led withwood shavings, and a weak so lu tion o f a lcoho l i sa l lowed to trick le S lowly through it . The l iqu idafter passing over the shavings comes ou t after anumber of hou rs wel l charged with acetic acid .

This process at fi rst sigh t appears to be a pu relychemical one

,and reminds u s of the oxidati on

which occu rs when alcohol i s al lowed to passover a platinum sponge . It has been claimed

,

i ndeed,that this i s a chemical oxidation i n which

bacteria p lay no part . But th is appears to be an


error. I t i s always fo und necessary in thi s methodto start the process by pouring upon the shavingssome warm vinegar. Unless in thi s way the shavi ngs become charged wi th the vi negar - holdingbacteria the alcoho l wi l l n o t undergo ox idationduring i ts passage over them

,and after the bac

teria thu s i ntroduced have grown enough to coatthe shav ings thoroughly the aceti c - acid production i s much more rapid than at fi rst . If vinegari s al lowed to trick le slowly down a suspendedstring, so that its bacteria may distribute themselves through the string, and then alcoho l be allowed to tri ck le over It in the same way , the ox idation takes place and acetic acid is formed . Fromthe accumulation of such facts i t has come to berecognised that al l processes for the commercialmanu factu re of vinegar depend upon the actionof bacteria . Whi le the oxidation of alcohol intoacetic acid may take place by pu rely chemicalmeans

,these processes are not practical on a large

scale,and v inegar manufacturers everywhere de

pend upon bacteria as thei r agents i n producingthe oxidation . These bacteria

,several spec ies in

al l,feed upon the n i trogenous matter in the fer

men ting mass and produ ce the desi red change inthe alcohol .This vinegar fermen tation i s subj ect to cer

tain i rregu lari ties,and the vinegar manufacturers

can no t alway s depend upon its occu rring in asatisfactory manner . Just as in brew i ng, so here,contaminating bacteria sometimes find thei r wayin to the fermenting mass and interfere with i tsn ormal course . In particu lar

,the flavou r of the

v i negar is l iable to su ffer from such causes . Asyet ou r v i negar manu factu rers have no t appl iedto acetic fermentation the same principle which


has been so successfu l i n brewing—namely,the

use,as a starter o f the fermentation

,of a pu re cu l

ture of the proper species of bacteria . This hasbeen done experimental ly and proves to be feasible . In practice

,however

,vinegar makers find

that simpler methods o f obtai n ing a starter—bymeans of which they procure a cu l tu re near lythough not abso l ute ly pu re—are perfect ly satisfacto ry . It i s u ncertain whether real ly pure cu ltu res wi l l ever be used in this industry .

L AC T IC AC ID .

The manu facture o f lactic acid i s an industryof less extent than that of acetic acid

,and yet i t

i s one which has some considerable commercialimportance . Lactic acid is u sed in n o large quanti ty

,al though i t i s of some value as a medicine

and in the arts . For i ts productio n we are whol lydependent upon bacteria . I t i s th is acid which

,

as we shal l see,i s produced in the o rdinary

souring of milk,and a large number of species

of bacteria are capable of producing the acidfrom milk sugar . Any sample of sour mi lk maytherefore always be depended upon to containplenty of lacti c organisms . In i ts manu facturefor commercial purposes mi lk i s sometimes usedas a source

,bu t more commonly other substances .

Sometimes a mixtu re of can e sugar and tartaricacid i s used . To start the fermentation the mixtu re is inocu lated with a mass of sou r mi lk or decay ing cheese , or both , such a mixture always contain ing lactic organisms . To be sure

,i t al so

contain s many other bacter ia which have diff erent eff ects

,but the acid producers are always so

abundan t and grow so vigorously that the lactic


fermentation occurs i n spi te of al l other bacteria .

Here also there i s a possibi l i ty o f an improvement in the process by the use of pu re cu ltures oflacti c o rgan isms. Up to the presen t , however,there has been no appl ication of such methods.The commercial aspects of the indu stry are notupon a suflicien t ly large scale to cal l fo r much inthis direction .

At the present t ime the on ly metho d we havefor the manu factu re of lactic acid i s dependen tupon bacteria . Chemical processes for its manufacture are known

,but not employed commer

cially . There are several di fferent kinds of lactic acid . They differ from each other in therelations of the atoms wi thin thei r mo lecu l e

,and

i n thei r relation to polari zed l ight,some forms

rotating the plane of polari zed l ight to the right,

others to the left,whi le others are inactive in thi s

respect . Al l the types are produced by fermentation processes

,di ff erent species of bacteria hav

ing powers o f producing the di fferent types .

BU T YRIC AC ID .

B uty ric acid i s another acid for wh ich we arechiefly dependen t upon bacteria . This acid is o fn o very great importance

,and i ts manufacture

can hardly be cal led an industry ; sti l l i t i s to acertain exten t made , and i s an article of commerce .

I t i s an acid that can be manu factured by chemicalmeans

,bu t

,as in the case of the last two acids

,i ts

commercial manufactu re i s based upon bacteria laction . Q u ite a number of species o f bacteriacan produce butyric acid

,and they produce i t from

a variety of di fferen t sources . Butyric acid i s acommon ingredient in o ld mi lk and in butter

,and

T HE USE OF BAC TERIA IN T HE ART S. 5 7

i ts formation by bacteria was historical ly one ofthe fi rst bacterial fermentations to be clear ly

.

umderst o o d. I t can be produced also in var ioussugar and starchy so lutions . G ly cerine may alsoundergo a bu tyric fermentation . The presenceof thi s acid is occasional ly t roublesome , since i ti s one of the factors i n the rancidity of butter ando ther simi lar materials .

INDIG O PREPARAT IO N .

T he preparation o f indigo from the indigo planti s a fermentati ve process brought about by a specific bacterium . The leaves of the plant are immersed i n water in a large vat, and a rapid fermentation arises . As a resu lt o f the fermentationthe part of the plant which is the basis of the indigo is separated from the leaves and di ssol ved inthe water ; and as a second featu re o f the fermentation the soluble material i s C hanged in i tsC hemical nature into indigo - proper . As thi sC hange occurs the C haracteristic b lue colour is dev elo ped, and the material i s rendered inso luble i nwater . I t therefo re makes i ts appearance as abl ue mass separated from the water

,and i s then

removed as indigo .

Of the natu re of the process we as yet knowvery l i tt le . That i t i s a fermentation is certain

,

and i t has been proved that i t i s produced by adefin i te species of bacteri um which occurs on theindigo leave s . If the steri l i zed leaves are placedin steri le water no fermentation occurs and noindigo is formed . I f

,however

,some of the spe

cific bacteria are added to the mass the fermentation soon begins and the blue colour O f the indigomakes i ts appearance . It i s p lai n

,therefo re

,that

5 8 T HE ST ORY O F G ERM L IFE.

i ndigo is a product of bacterial fermentation , andcommon ly due to a single definite species of bacterium. Of the detai ls of the formation

,however

,

we as yet know l i tt le,and no practical appl ica

t ion of the facts have yet been made .

BAC T ERIA IN T O BAC C O C URING .

A fermentati ve process of qu i te a di ff erent natu re

,bu t of immense commercial value

,i s fo und

i n the p reparatio n of tobacco . The process bywhich tobacco i s prepared is a long and somewhat complicated one

,consisting o f a number of

di fferent stages . The tobacco,after being fi rst

dried in a carefu l manner,i s subsequently al lowed

to absorb mo istu re from the atmosphere,and i s

then placed in large heaps to undergo a furtherchange . This process appears to be a fermentation

,for the temperatu re of the mass rises rapid ly

,

a nd every indication of a fermentative action isseen .

°

The tobacco i n these heaps i s changedoccasional ly

,the heap being thrown down and

bui l t up again i n such a way that the port ionwhich was fi rst at the bottom comes to the top

,

and i n th is way al l parts o f the heap may become equal ly affected by the process . After thisprocess the tobacco is sent to the di fferent manufacturers

,who fin ish the process of cu ring . The

further treatment i t receives varies widely ac

cording to the desi red product,whether fo r smo k

i ng o r for snu ff,etc . In al l cases

,however

,

fermentation s p lay a prominent part . Sometimes the leaves are di rect ly inocu lated with fermen ting material . In the preparation of snu ffthe detai l s of the process are more compl icatedthan in the preparation of smoking tobacco . The


appear to be produ ced by mi cro - organ isms ofdi ff erent so rts . During the fermentation whichfol lows the drying the producer has to contendwith micro - organ isms that are troublesome to himfor un less the phenomena are proper ly regu latedthe fermentation that occu rs produces e ff ectsupon the tobacco which ru in i ts characte r . Fromthe time the tobacco i s o ut u n ti l the final stagei n the cu ring the persons engaged in preparingi t fo r market must be on a constant watch toprevent the growth withi n i t of undesi rable o r

gan isms. The preparation of tobacco i s for th i sreason a del icate O peration

,and one that wi l l be

very l ikely to fai l u n less the greatest care i s taken .

I n the severa l fermentative processes whichoccur in the preparation there i s n o quest ion thatmicro - organi sms aid the tobacco producer andmanufactu rer . Bacteria produce the first fermenta f ion that fo l lows the drying, and i t i s these o r

gan isms too, i n large measure, that give ri se toal l the subsequen t fermentations, al tho ugh seemingly i n some cases pu rely C hemical processesmaterial ly aid . No w the special qual ity O f thetobacco is in part dependen t upon the pecu liartype of fermentation which occu rs in one or another of these fermenting actions. I t i s the fermentation that gives r i se to the pecu l iar flavou rand to the aroma of the di fferen t grades of tobacco .

I nasmuch as the variou s flavours which C haracf erize tobacco of di fferen t grades are developed

,

at least to a large extent,du ring the fermentation

processes,i t i s a natu ral supposi t io n that the di f

feren t qual ities of the tobacco,so far as concerns

flavou r,are due to the differen t types of fermen

tatio n . The number of species o f bacteria whichare found upon the tobacco leaves i n the various

T HE USE OF BAC T ERIA IN T HE ART S. 6 1

stages of its preparation i s qu i te large,and from

what we have already learned i t i s inevi table thatthe di ff erent kinds of bacteria wi l l produce di fferen t resu l ts i n the fermenting process . I twou ld seem natu ral

,therefore

,to assume that the

different flavours o f di fferen t grades may not unl ike ly be due to the fact that the tobacco in thedi fferen t cases has been fermen ted under the influence of di fferen t kinds of bacteria .

Nor is thi s simply a matter of inference . To acertain extent experimental evidence has borne o utthe concl usion

,and has given at least a sl ight in

dicat io n of practical resu l ts in the fu ture . Actingupon the suggestion that the di fference betweenthe high grades of tobacco and the poorer gradesis due to the character of the bacteria that produce the fermentation

,certain bacterio logists

have attempted to obtain from a high qual i ty oftobacco the species of bacteria which are in festingit . These bacteria have then been cu l ti vated bybacterio logical methods and u sed i n experimentsfor the fermentation of tobacco . I f i t i s true thatthe flavour of high grade tobacco i s in large measu re , or even in part, due to the action of the peculiar microbes from the so i l where i t grows

,i t

ought to be possible to produce simi lar flavoursin the leaves of tobacco grown in other local i t ies

,

i f the fermentation of the leaves i s carried o n bymeans of the pure cu ltu res of bacteria obtainedfromthe high grade tobacco . Not very much hasbeen done or i s known in this connection as yet .T wo bacteriologi sts have experimented independently in fermen ting tobacco leaves by the actionof pure cu ltures o f bacteri a obtained from suchsources. Each of them reports successfu l experimen ts . Each C laims that they have been able to


improve the qual i ty of tobacco by inocu lating thel eaves wi th a pu re cu l tu re of bacteria obtainedfrom tobacco having high qual i ty in flavou r. Inaddi tion to thi s

,several other bacterio logists have

carried on experiments su fficient to indicate thatthe flavou rs of the tobacco and the character o fthe ripening may be decidedly changed by the useof di fferent species o f micro - organisms in the fermentations that go o n du ring the cu ring processes .

In regard to the whole matter,however

,we

must recognise that as yet we have very l i t tleknowledge. The subj ect has been under investi

gatio n fo r on ly a Short time ; and, whi le co n sid

e t abl e info rmation has been derived,this in fo r

mation i s no t tho roughly u nderstood,and ou r

knowledge in regard to the matter is as yet inra ther a chaotic condition . I t seems certain

,

however,that the qual i ty o f tobacco is in large

measu re dependent upon the character o f the fermentations that occu r at different stages o f thecu ring. I t seems certain also that these fermentatio ns are who l ly or chiefly produced by microo rganisms

,and that the C haracter o f the fermen

tat io n i s i n large measu re dependent upon thespecies of micro - organisms that produce i t . I fthese are facts

,i t would seem not improbable

that a fu r ther study may produce practica l re

sults for th i s great industry . The study of yeastsand the methods of keeping yeast from contamin ations has revo l u tion ised the brewing industry .

Perhaps in this o ther fermentative industry,which

i s o f such great commercial extent , the use ofpu re cu ltu res o f bac teria may i n the future produce as great revolutions in methods as i t has inthe industry o f the alcohol ic fermen tation .

I t must not,however

,be inferred that the di f

T HE USE OF BAC T ERIA IN T HE ART S. 63

terences in grades of tobacco grown in di fferentparts of the world are due so lely to variations i nthe curing processes and to the types of termentatio n . There are di fferences in the texture ofthe leaves

,d ifferences in the chemica l composi

tion of the tobaccoes, which are due u ndoubted lyto the so i l s and the C l imatic conditions in whichthey grow

,and these

,of course

,wi l l never be af

fected by changing the character of the fermentative processes . I t i s

,however

,probable that in

so far as the flavours that distingu ish the high andlow grades of tobacco are due to the character o fthe fermentati ve processes, they may be in the fut u re

,at least to a large ex tent

,con tro l led by the

use of pu re cu ltu res in curi ng processes . Seemingly , then , there is as great a fu tu re in the develo pmen t of this fermentative industry as therehas been in the past in the developmen t of thefermentative industry associated with brewingand vinting.

O PIUM.

Opium for smoking purposes i s commonlyal lowed to undergo a curing process which lastsseveral months . This appears to be somewhatsimi lar to the cu ring of tobacco . Apparently i ti s a fermentatio n due to the growth of mi croo rgan isms . The organisms in question are not

,

however,bacteria i n this case

,but a species o f

al l ied fungus . The plant is a mou ld,and i t i s

claimed that inocu lation of the opi um wi th cu ltures of this mou ld hastens the cu ring.

T RO UBL ESOME FERMENT AT IONS.

Befo re leaving th is branch of the subj ect i t i snecessary to notice some of the troublesome fer


men tations which are ever interfering with o ur

i ndustries,requ ir ing special methods

,or

,i ndeed

,

sometimes developing specia l industries to meetthem . As agents O f decomposition

,bacteria Wi l l

o f course be a trouble when ever they get intomaterial which i t i s desi red to preserve . Sin cethey are abundant everywhere, i t i s necessary tocount u pon thei r attacking wi th certain ty an yfermentable substance which is expo sed to ai rand water. Hence they are frequent ly the cau seo f much trouble . In the fermentative industriesthey occasional l y cause an improper sort of fermentation to occu r un less care i s taken to preven t undesi red species of bacteria from beingpresent . In v i negar mak ing

,improper species o f

bacteria obtaining access to the so lu tion giverise to undesi rable flavours, great ly in j u ring theproduct . In tobacco curing i t i s very commonfor the wrong species o f bacteria to gain accessto the tobacco at some stage of the cu ring andby thei r growth give rise to various troubles .I t i s the ubiqu i tou s presence of bacteria whichmakes i t impossible to preserve fru its, meats, orvegetables for any length of time withou t specialmethods . This fact in i tsel f has cau sed the develo pmen t of one of o ur most important industries . Canning meats o r fru i ts consists i n nothing more than bringing them into a condition inwhich they will be preserved fromattack of thesemi cro - organ isms . The method is ex tremely simple in theory . I t i s nothing more than heatingthe material to be preserved to a high temperatu re and then seal ing i t hermetica l ly whi le i t isst i l l hot . The heat ki l l s al l the bacteria whichmay chance to be lodged in i t, and the hermeticalseal ing prevents other bacteria from obtaining

T HE USE OF BAC T ERIA IN THE ART S. 65

access. Inasmuch as al l o rgan ic decomposi tioni s produced by bacteria l growth

,such steri l i zed

and sealed materia l wi l l be preserved indefin itelywhen the operation i s performed care fu l ly enough .

The methods of accompli shing this with su fficien tcare are somewhat varied in differen t industrie s

,

but they are al l fu ndamental ly the same . I t i san i n teresting fact that th is method of preservingmeats was devised in the last cen tu ry

,before the

relation of micro - organ i sms to fermentation andputrefaction was real ly suspected . For a longtime i t had been in practica l u se whi le scientistswere sti l l disputing whether pu trefaction cou ld beavoided by preventing the access o f bacteria. Theindustry has

,however

,developed wonderfu l ly

with in the last few years,si nce the principles

underlying i t have been understood . This un

derstanding has led to better methods o f destroying bacteria l l i fe and to proper sealing

,and these

have of course led to greater success in the preservatio n ,

unti l tod ay the canning industries areamong those which invo lve capital reckoned inthe mi l l ions .Occasional ly bacteria are of some va lue i n

food products. The gamy flavour o f meats i snothing more than i ncipient decomposi t ion .

Sauer K raut i s a food mass intentional ly al lowedto fermen t and sour. The val ue of bacteria inproducing butter and cheese flavou rs i s noticedelsewhere . But common ly our aim must be topreven t the growth of bacteria i n foods. Foodsmust be dried o r cooked o r kept on ice, or someother means adopted fo r prevent i ng bacterialgrowth i n them . I t is their presence that forcesu s to keep our ice box

,thus founding the ice

business as wel l as that of the manufactu re of


refrigerators . It i s thei r presence,again

,that

forces u s to smoke hams,

’

to sal t mackere l,to dry

fi sh o r other meats,to keep pork i n brine

,and to

in troduce n umerous other detai l s in the methodsof food preparation and preservation .

CHAPTER III .

REL AT ION OF BAC T ERIA T O T HE DAIRY

INDUST RY.

DA IRYING i s one o f the most primitive o f ou rindustr ies . From the very earl iest period

, eversince man began to keep domesti c cattle, he hasbeen fami l iar with dairying .

‘

During these manycen tu ries certai n methods of procedu re havebeen developed which produce desi red resu l ts.These methods

,however

,have been dev ised sim

ply from the accumu lation of experience,with

very l i tt l e knowledge as to the reasons underlying them . The methods of past cen tu ries are,however

,ceasing to be sati sfactory . The ad

vance of o ur C i v i l i zation during the last halfcentu ry has seen a marked expansion in the exten t O f the dai ry indu stry . With this expansionhas appeared the necessi ty for new methods, anddairymen have for y ears been looking for them .

The last few years have been teaching us thatthe new methods are to be found along the l ineof the appl ication of the discoveries of modernbacter iology : We have been learn ing that thedai ryman i s more closely related to bacteria andthei r activi ties than almost any other C lass o fpersons. Modern dairying

,apart from the mat


teria are not present,i t wi l l remain sweet indefi

n ite ly.

Bu t i t i s impossible to draw mi lk from theco w i n such a manner that i t wi l l be free frombacteria except by the use o f precautions absolutely impracticab l e in ordinary dairying. As

milk i s commonly drawn,i t i s su re to be contami

n ated by bacteria , and by the time i t has enteredthe mil k pai l i t contains frequen t ly as many ashal f a mi l l ion , or even a mi l l ion , bacteria i n everycubic inch of the mi lk . This seems almost incredible

,but i t has been demonstrated in many

cases and i s beyond quest ion . Since these bacteria are n o t i n the secreted mi lk

,they must

come from some external sources,and these

sou rces are the fol lowingThe first i n importance is the cow hersel f ;

fo r whi le her mi l k when secreted i s steri le,and

whi le there are no bacteria i n her blood,neverthe

l ess the cow is the most prol ific source of bacteria l con tamination . In the first p lace

,the mi lk

ducts are ful l o f them . After each milk ing a l i tt le mi lk i s always left i n the duct

,and this fur

n i shes an ideal p lace fo r bacteria to grow. Somebacteria from the ai r or elsewhere are su re toget into these ducts after the mi l king

,and

they begin at once to multiply rap idly. By thenext milk ing they become very abundan t in theducts

,and the fi rst mi lk drawn washes most of

them at once into the mi l k pai l,where they can

continue thei r growth i n the mi l k . Again,the

exterior o f the cow ’s body contains them inabundance. Every hair, every particl e of di rt,every b i t o f dried manu re, i s a lu rk ing place fo rmi l l ions of bacteria . The hind quarters of aco w are commonly in a condi tion of much fil th,

RELAT ION OF BAC T ERIA T o DAIRY INDUSTRY. 69

for the farmer rarely grooms hi s co w,and during

the mi lking,by her movements

,by the swi tching

of her tai l,and by the rubbing she gets from the

mi lker,n o i nconsiderable amount of this dirt and

fi l th i s brushed o ff and fal ls in to the mi lk pai l .The farmer understands th i s source of dirt andusual ly feel s i t necessary to strain the mi lk afterthe mi lking. But the straining i t receives througha coarse cloth

,whi le i t wi l l remove the coarser

particles of di rt,has no effect upon the bacteria ,

for these pass through any strainer u n impeded .

Again,the mi lk vessel s themselves contain bac

teria,for they are never; washed absolu te ly clean .

After the most tho rough washing which the mi lkpai l receives from the kitchen

,there wi l l a lways

be left many bacteria cl inging in the cracks of thet in or in the woo d

,ready to begin to grow as

soon as the mi lk once more fi l l s the pai l . Themi lker himsel f contributes to the suppl y

,for he

goes to the mi lking with uncl ean hands,unclean

C lo thes,and not a few bacteria get from him to

his mi l k pai l . Lastly,we find the ai r o f the mi lk

ing stall fu rn ishing it s quota o f mi lk bacteria .

This source of bacteria i s,however

,not so great

as was formerly bel ieved . That the ai r may contain many bacteria i n its dust i s certain

,and

doubtless these fal l in some quanti ty in to themi lk

,especial ly i f the catt le are al lowed to feed

upon dusty hay before and during the mi lk ing .

But unless the ai r i s thu s fu l l o f dust thi s sourceof bacteria i s not very great

,and compared with

the bacteria from the other sources the ai r bacteria are u n importan t .The mi lk thus gets fi l l ed with bacteria

,and

since i t furn ishes an excel len t food these bacteriabegin at once to grow . The mi lk when drawn i s

70 T HE STORY O F G ERM L IFE.

warm and at a temperatu re which especial lystimu lates bacterial growth . They mu l t iply withgreat rapidity

,and in the cou rse of a few hours

increase perhaps a thousandfo ld . The numberswhich may be found after twenty - fo u r hours aresometimes inconceivable ; market mi lk may contain as many as five hundred mi l l ion s per cubici nch ; and whi le this i s a decidedly ext reme number

,mi lk that i s a day o ld wi l l almost a lway s

contain many mi l l ions in each cubic inch,the

number depending upon the age o f the mi lk and

i ts temperatu re. During this growth the bacteriahave

,o f course

,not been w i thou t thei r effect .

Recognising as we do that bacteria are agents forC hemical C hange

,we are prepared to see the milk

undergoing some modifications during this rapidmu ltip l ication o f bacteria. The C hanges whichthese bacteria produce in the mi lk and i ts prodn o ts are numerou s

,and decidedly affect i ts val ue .

They are both advan tageo us and disadvan tageousto the dai ryman . They are nuisances so far asconcern s the mi lk producer

,but al l ies of the bu t

ter and cheese maker.

T HE EFFEC T O F BAC T ERIA ON MIL K .

The first and most un iversal change effectedin mi lk i s i ts so uring . So un iversal i s thi s phen omen o n that i t i s general ly regarded as an inevi table change which can not be avo ided

,and

,as

already pointed out, has in the past been regardedas a normal property o f mi lk . To - day

,however

,

the phenomenon i s wel l u nderstood . I t i s due tothe action of certain o f the mi lk bacteri a uponthe mi lk sugar which co nverts i t in to lactic acid

,

and this acid gi ves the sou r taste and curd les

RELAT ION OF BAC T ERIA T o DAIRY INDUST RY. 7 1

the mi lk . After th is acid is produced i n smal l

quanti ty i ts presence proves de leterious to thegrowth of the bacteria

,and fu rther bacterial

growth is C hecked . After sou ring, therefo re, themilk for some time does no t o rdinari ly undergoany further changes .Milk souring has been common ly regarded as

a si ngle phenomenon,alike in al l cases. When i t

was fi rst studied by bacterio logists i t was though tto be due in al l cases to a single species o f microorgan ism which was di scovered tobe commonly present and namedBacillus acz

'

di lactz'

ci (Fig . Thisbacterium has certain ly the power aof sou ring mi lk rapid ly

,and is

found to be very common in dairies in

.

Europe . As soon as bacte FIG . 19. Baa-

”wrio lo gists tu rned the ir attention the

more closely to the subj ect i t was “mm?“Pauseo f so urmilk.

found that the spontaneou s so u ring of mil k was not always cau sed by the samespecies of bacterium. Instead of finding this Ba

cillus acidi lactz'

ci always presen t,they found that

qu i te a number of differen t species of bacteriahave the power of so uring mi lk

,and are found in

differen t specimens of so ured mi lk . The n umberof species of bacte ria which have been found tosou r mi lk has increased unti l something over ahundred are kno wn to have this power. Thesedi ff erent species do not aff ect the mi lk in thesame way . Al l produce some acid

,but they

di ffer in the k ind and the amount of acid , andespecial ly i n the other C hanges which are effectedat the same time that the mi lk i s soured

,so that

the resu lt ing soured mi lk i s qui te variable . Inspi te of thi s variety

,however

,the most recent

72 THE ST ORY OF GERM L IFE.

work tends to show that the majori ty o f cases ofspon taneous souring o f mi lk are produced bybacteria which

,though somewhat variable

,prob

ably consti tu te a single species,and are iden tical

with the B acillus acidi lactici (Fig. This species

,fo und common in the dai ries of Eu rope

,ao

cording to recen t investigations occu rs in thi scountry as wel l . We may say, then , that whilethere are many species of bacteria infesting thedai ry which can sour the milk

,there i s one which

is more common and more u nive rsal ly found thanothers

,and this i s the ordinary cause o f mi lk

so u ring.

When we st udy more carefu l ly the effect uponthe mi l k of the diff erent species of bacteria foundin the dai ry

,we find that there i s a great variety

of changes which they produce when they are allowed t o grow in mi lk . The dairyman expe

riences many troubles with his mi lk . I t sometimescurdles withou t becoming acid . Sometimes i tbecomes bitter

,or acqui res an unp leasant tain ted

”

taste,o r

,again

,a “so apy taste. Occasion al ly a

dai ryman finds hi s mi l k becoming slimy ,i n stead of

sou ring and cu rdl ing i n the normal fashion . Atsuch times

,after a number of hours

,the mi lk be

comes So sl imy that i t can be drawn into longthreads . Such an in fection proves very troublesome

,fo r many a time it persi sts i n spi te of al l

attempts made to remedy i t . Again, in othercases the mi lk wi l l tu rn blue

,acqui ring abou t the

time i t becomes sour a beauti fu l Sky - blue co lour.Or i t may become red

,or occasional ly y ellow . Al l

of these troubles the dai ryman owes to the presence in his milk of unusual species o f bacteriawhich grow there abun dantly .

Bacterio logists have been ab le to make o ut

RELAT ION OF BAC T ERIA T O DAIRY INDUST RY. 73

sati sfactori ly the co nnection o f al l these in teet ion s wi th differen t species o f the bacteria. Alarge number of species have been found to curdle mi lk wi thout rendering i t acid

,several render

i t bitter,and a number produce a

tainted and one a soapytaste . A score o r more have beenfound which have the power o frendering the mi lk sl imy . Twodi fferen t species at least have the 0power of tu rning the mi lk to sky FIG . 2o .

—Dairy 6acblu e co lour ; two or three pro ig

u

n

‘

fufifwumg

'

duce red pigments (Fig. andone or two have been found which produce a ye llo w co lo ur . In short, it has been determined beyond question that al l these in fection s, which aremo re o r less troublesome to dairymen , are dueto the growth of unusu al bacteria i n the mi lk .

These variou s infections are al l t roublesome,

and indeed it may be said that,so far as concerns

the mil k producer and the mi lk consumer, bacteria are from beginning to end a sou rce of t rouble . I t i s the desire of the mi lk producer toavoid them as far as possible—a desi re which i sshared also by everyone who has anything to dowith mi lk as mi lk . Having recognised that thevario us tro ubles

,which occasional ly occu r even

i n the better class of dairies,are due to bacteria ,

the dai ryman i s,at least in a measu re

,prepared

to avoid them . The avoiding of these troublesi s moderately e asy as soon as dairymen recognise the source from which the in fect io n s o r

gan isms come, and also the fact that lo w temperatures wil l in al l cases remedy the evi l to alarge exten t . With this knowledge in hand the

’

avoidance of al l these tro ubles i s on ly a question


of care i n handl ing the dairy . I t must be recogn ised that most of these troublesome bacteriacome from some unu sual sou rces o f i nfection .

By unusual sources are mean t those which the excrcise of care wi l l avoid. I t is true that the souri ng bacteria appear to be so u n iversal ly distribu ted that they can no t be avoided by any ord inarymeans . But al l other troublesome bacteria appear to be with in con trol . The mi lkman mustremember that the sou rces of the troubles whichare l iable to arise in hi s mi lk are in some fo rm offi l th : ei ther fi l th on the cow

,or dust in the hay

which i s scattered through the barn,or di rt o n

cows ’ udders,or some other unusual and avoid

able source . These sou rces,from what we have

al ready noticed,wi l l a lways furnish the mi lk wi th

bacteria ; bu t under common condi tions, and whenthe co w i s kept i n conditions of ordinary clean li

ness,and frequent ly even when not clean ly

,wil l

on ly fu rni sh bacteria that produce the u n iversa lsou ring. Recogni sing th is

,the dai ryman at once

learns that his remedies for the troublesome infect io n s are clean l iness and low temperatu res.

If he i s carefu l to keep his mi lk vesse ls scrapu

lo usly clean ; i f he wi l l keep h is cow as clean ly ashe does his horse ; and i f he wi l l u se care i n andaround the barn and dai ry

,and then apply low

temperatures to the mi lk , he need never be disturbed by sl imy or tain ted mi lk , or any o f theseo ther tro ubles ; or he can remove such infection sspeedi ly shou ld they once appear. Pure sweetmi lk is only a question of su fficient care . Bu tcare mean s labour and expense . As long as wedemand cheap mi lk , so long wi l l we be supp l iedwith milk procured under conditions of fi l th . Bu twhen we learn that C heap mi lk is poor mi lk , and

76 T HE ST ORY O F GERM L IFE.

i s desi red,and the cream is sub j ected to a process

known as “r ipening or “sou ring before i t i schu rned . I n ripen ing

,the cream is simply al

lowed to stand in a vat for a period varyingfrom twelve hours to two o r three days

,accord

ing to ci rcumstances. During this period certainC hanges t ake place therein . The bacteria whichwere in the cream original ly

, get an opportun i tyto grow

,and b y the time the r ipeni ng is complete

they become extremely numerous . As a resu l t,

the character o f the cream changes j ust as themi l k i s changed under simi lar ci rcumstances. I tbecomes somewhat soured ; i t becomes sl ight lycu rdled

,and acqu i res a pecu l iarly pleasant taste

and an aroma which was not present in the original fresh cream . After this ripening the creamis ch u rned . I t is during the ripen ing that thebacteria produce thei r effect

,for after the C hu rn

ing they are of less importance . Part of themcol lect i n the butter

,part of them are washed o ff

from the bu tte r in the buttermi lk and the subse

quent processes. Most of the bacteri a that areleft i n the bu tter soon die, no t finding there afavourable condition for growth ; some of them,

however,l ive and grow for some time and are

prominen t agents in the C hanges by which bu tterbecomes rancid . The butter maker i s concernedwith the ripening rather than with later processes .The obj ect o f the ripen ing of cream is to render

i t in a better condit ion fo r butter making. Thebutter maker has learned by long experience thatripened cream churn s more rapid ly than sweetcream

,and that he obtains a larger yie ld of bu tter

therefrom . The great object of the ripen ing,

however,i s to develop in the butter the pecul iar

flavo ur and aroma which is characteri stic o f the

RELAT ION O F BAC T ERIA T o DAIRY INDUST RY. 77

h ighest product . Sweet cream butter lacks flavou r and aroma

,having indeed a taste a lmost

identical ly the same as cream . Butter,however

,

that is made from ripened cream has a pecu liardel icate flavou r and aroma which i s wel l known tolovers of butter

,and which is developed during

the ripening process .Bacterio logi sts have been able to expl ain wi th

a con siderab le degree of accu racy the obj ect oft his ripening. The process i s real ly a fermentat ion comparable to the fermen tation that takesplace i n a brewer

’s malt . The growth of bacteriadu ring the ripening produces C hemical changesof a somewhat compli cated character, and concerns each of the ingredients of the mi lk . Thelactic - acid organ i sms aff ect the mi lk sugar andproduce lacti c acid ; others act upon the fat, producing sl ight changes therein ; whi le o thers actupon the casein and the albumen s o f the mil k .

As a resu lt,various b ipro ducts of decomposi tion

ari se,and it i s these bipro ducts of decomposi tion

that make the difference between the ripened andthe un ripened cream . They render i t sou r andcurdle i t

,and they also produce the flavours and

aromas that characteri ze i t . Products of decomposi tion are general ly looked upon as undesirablefor food

,and this i s equal ly tru e of these products

that arise i n cream if the decomposi tion i s al lowedto contin ue long enough . I f the ripen ing

,i n stead

of being stopped at the end of a day or two,i s

al lowed to conti nue several days,the cream be

comes decayed and the butter made therefrom isdecidedly offensive . Bu t under the condition s ofordi nary ripening, when the process i s stopped atthe righ t moment

,the decomposit ion products

are pleasan t rather than u npleasant,and the fla


Yours and aromas which they impart to the creamand to the subsequen t butter are those that aredesi red . I t i s these decomposition products thatgive the pecu l iar C haracter to a high qual i ty ofbutter

,and this pecu l iar qual i ty i s a matter that

determines the price which the butter maker canobtai n for hi s product .But

,u nfo rtunately, the bu tter maker i s no t al

ways able to depend upon the ripening . Whilecommon ly i t progresses i n a satisfactory mann er

,

sometimes,fo r no reason that he can assign

,the

r ipening does n o t progress no rmal ly . Instead ofdeveloping the pleasant aroma and flavour of theproper ly ripened cream

,the cream develops nu

pleasan t tastes . It may be bi tter o r somewhattain ted

,and j u st as sure as these flavours develop

i n the cream,so sure does the quali ty of the but

ter su ffer . Moreover,i t has been learned by ex

perience that some creameries are incapable ofobtain ing an equal ly good ripening of their c ream .

Whi le some of them wi l l O btain favourable resu lts,

others,with equal care

,wi l l Obtain a far less favour

able flay o ur and aroma in their butter . The reason for al l thi s has been explained by modern bacterio lo gy . In the mi lk

,and consequen tly i n the

cream,there are always found many bacteria

,b ut

these are not always of the same kinds . Thereare scores

,and probably hundreds

,of species o f

bacteri a common in and around our barns anddai ries

,and the bacteria that are abu ndant and

that grow in different lo ts of cream wi l l no t bea lways the same . I t makes a decided differencein the character of the ripening

,and in the co n se

quent flavours and aromas,whether one or another

species o f bacteria has been growing in the cream .

Some species are fo und to produce good resu l ts

REL AT ION OF BAC T ERIA T O DAIRY INDUSTRY. 79

with“

desi red flavou rs, whi le others, un der iden ticalcondi tions

,produce decidedly poo r resu l ts with

undesired flavou rs (Figs . 2 1 If the bu ttermaker obtain s creamwhich is fi l led with a largenumber of bacteria capable of producing goodflavours

,then the ripening o f his cream wi l l be

sati sfactory and his bu tter wi l l be o f high qual i ty .

If,however

,i t chances that his cream contain s

only the species which produce unp leasan t flavours

,then the character o f the ripening wi l l be

decidedly in ferio r and the butter wi l l be of apoorer grade . Fortunately the majori ty of thekinds of bacteria l iable to get into the creamfrom ordinary sources are such as produce ei thergood effects upon the cream or do not material lyi nfluence the flavour or aroma . Hence i t i s thatthe ripening of cream wi l l common ly producegood resu l ts. Bacteriologists have

'

learn ed thatthere are some ' species o f bacteria more o r lesscommon around ou r barns which produce undesi rable effects upon fl avour, and shou ld these become especial ly abu ndan t in the cream

,then the

character of the ri pening and the qual i ty o f thesubsequen t butter wi ll su ffer. These malign species of bacteria , however, are no t very common inproperly kept barns and dai ries . Hence the process that i s so widely used

, O f simply al lowingcreamto ripen under the influence o f any bacter ia that happen to be in i t

,ordinari ly produces

good resu l ts. But our butter makers sometimesfind

,at the times when the catt le C hange from

winter to summer o r from summer to winter feed,

that the r ipening is abnormal . The reason appears to be that the cream has become in festedwith an abundance of mal ign species . The ripening that they produce is therefore an undesi rable


o n e,and the qual ity of the butte r is su re to

suffer.So long as bu tter was made on ly in private

dai ries it was a matter O f comparatively l i ttl eimportance if there was an occasional fall ing o ff

in qual ity of thi s so rt. Wheni t was made a few poundsat a time

,and on ly once or

twice a week,i t was not a

very serious matter i f a fewchu rn ings o f butter did suffer in qual i ty . But to - daythe butter- making industries

FIG ent

- Dairy bacterium are becoming more and more

gmc’

ggbefi

t

fi‘

g concentrated into largespecies has been used creameries, and i t i s a matwmmem‘auY f“the“P“ ter of a good deal more imen ing o f cream.

portance to discover somemean s by which a uniformly high quali ty can bein su red . I f a creamery which makes five hundred pou nds of bu tter per day suffers from suchan in j u rio u s ripening

,the qual i ty o f i ts but

ter wi l l fal l o ff to such an extent as to commanda lower price

,and the creamery su ffers material

ly . Perhaps the con tin uation of such a troublefo r two or three weeks wou ld make a di fferencebetween fi nancial success and fai l ure i n the creamery. With our concentration of the butter - making industri es i t i s becoming thus de si rable tod iscover some means of regu lating this processmore accurate ly .

The remedy o f these occasional i l l effects i ncream ripening has n o t been wi thin the reach ofthe butter maker. The butter maker mu st makebutter with the cream that i s furni shed him

,and

i f that cream is already impregnated with mal ign

RELAT ION OF BAC T ERIA T o DAIRY INDUSTRY. 8 1

species o f bacteria he i s helpless . I t i s true thatmuch can be done to , remedy these difficul t ies bythe exerci se of especial care in the barns of thepatrons of the creamery . I f the barns

,the cows

,

the dairies,the mi lk vessels

,etc . ,

are al l kept incondition o f strict clean l iness

,i f especial care i s

taken particu larly at the seasonsof the year when trouble 1s l i kely ato arise

,and i f some atten tion i s

paid to the kind of foodwhich the 0catt le eat

,as a ru le the cream wi l l

not become infected with 1njurio us Fl

géctn Dairy

bacteria . I t may be taken as aducifl

‘

g‘mgleaggg

demonstrated fact that these ma aroma In butter.

lign bacteria come from sources offi l th

,and the carefu l avoidance of al l such sou rces

o f fi l th wi l l i n a very large measure prevent thei roccurrence in the cream . Such measu res as thesehave been found to be practicable i n many creameries . Creameries which make the highest pricedand the most un iform quali ty of bu tter are thosei n which the greatest care i s taken in the barnsand dai ries to insu re clean liness and in the handling of the mi lk and cream . With such attentiona large portion of the trouble which arises in thecreameries from malign bacteria may be avo ided .

But these methods fu rn ish no su re remedyagainst evi l s o f improper species of bacteria incream ripening

,and do no t furn ish any su re

means of obtaining uni form flavou r i n butter .Even under the very best conditions the flavouro f the butter wi l l vary with the season o f the

y ear. Butter made in the winter i s inferior tothat made in the summer months ; and whi le thi si s doubt less due i n part to the di fferen t foodwhich the cattle have and to the character o f the

6


cream resu l ting therefrom,these di fferences in

the flavo u r of the butter are also in part dependent upon the different species o f bacteria whichare presen t i n the ripening of cream at di fferentseasons. The species o f bacteri a in June creamare different from those that are common ly present in January cream , and thi s i s certain ly a facto r i n determin ing the di fference between winterand summer butter.

USE O F ART IFIC IAL BAC T ERIA C U L T URES FOR

C REAM RIPENING .

Bacterio logists have been for some time endeavo uring to aid butter makers in thi s d irectionby furnishing them with the bacteria needfu l forthe best resu lts i n cream ripen ing. The methodof doing thi s i s extremely simple in princip le

,bu t

proves to be somewhat di fficu lt in practice . I t i son ly n ecessary to obtain the species of bacteriathat produce the highest resu lts

,and then to fu r

n ish these in pu re cu l tu re and in large quanti tyto the butter makers

,to enable them to in o cu

l ate thei r cream w i th the species o f bacteriawh ich wi l l produce the resu lts that they desi re .

For th is pu rpose bacterio logists have been fo rseveral years searching fo r the proper species ofbacteria to produce the best resu lts

,and there

have been pu t upon the market fo r sale severa ld i stinct “pure cultures for thi s pu rpose . Thesehave been obtained by differen t bacterio logistsand dai rymen in the northern Eu ropean coun triesand also in the United States . These pu re cu lt u res are fu rn i shed to the dai rymen in variou sforms

,but they alway s consist of great quant i

t ies of certain k inds of bacteria wh ich experience

84 T HE ST ORY OF GERM L IFE .

ed cult ure alone . This method proves to be successful, and in the butter -making countries inEurope i t is becoming rapid ly adopted .

In thi s country,however

,th i s process has

n o t as yet become very popular,i nasmuch as the

heating of the cream is a matter o f considerableexpense and trouble

,and ou r butter makers have

not been very ready to adopt i t . For this reason,and also for the pu rpose of fami l iari z ing buttermakers wi th the use of pu re cu l tu res

,i t has been

attempted to produce somewhat simi lar thoughless un i form resu l ts by the u se of pu re cu ltu resi n cream without previous heal ing. In the u seof pure cu l tures in this way

,the butter maker is

di rected to add to his cream a large amount ofa prepared cu l tu re of certain species of bacteria,upon the pr in cipl e that the addition o f such alarge n umber of bacteria to the cream, eventhough the cream is al ready inocu lated wi thcertain bacteria

,wi l l produce a ripening of the

cream chiefly infl uenced by the artificial ly addedcu l ture. The cu lture thu s added

,being presen t

i n very much greater quanti ty than the other“wi ld species

,wi l l have a much greater effect

than any of them . This method,of co urse, can

not insu re uni fo rmi ty . Whi le it may work satisfacto rily i n many cases, i t i s very eviden t that inothers

,when the cream is al ready fi l l ed with a

large number of mal ign species of bacteria, suchan artificial cu l ture wou ld not produce the desi redresu l ts . This appears to be no t on ly the theore tical bu t the actual experience . The addit iono f such pure cu ltu res i n many cases producesfavou rable resu l ts

,but i t does not always do so ,

and the resu l t i s no t un i form . While the use o fpu re cu ltures i n this way i s an advan tage over


the method of simply al lowing the cream to ripennormal ly withou t such addi tions

,i t i s a method

that i s decidedly in ferio r to that which fi rstpasteu rizes the cream and subsequen t ly adds astarter .There is st i l l another method of adding bac

teria to cream to in su re a more advantageousr ipen ing

,which is frequently used

,and, being

simpler,i s i n many cases a decided advan tage .

Thi s method i s by the u se o f what i s cal led anatural starter . A natu ra l starter consi sts simplyof a lo t of cream which has been taken from themost favourable source possib le— that i s, fromthe cleanest and best dairy

,o r from the herd

producing the best qual i ty of cream—and al lowing this cream to stand in a warm place for a

couple of days unti l i t becomes sou r . The creamwi l l by that time be fi l led with large numbers ofbacteria

,and thi s i s then pu t as a starter in to the

vat of cream to be ripened . Of cou rse, i n the useof this method the butter maker has no con tro lo ver the kinds of bacteria that wi l l grow in thestarter

,but it i s found

,practical ly

,that i f the

cream is taken from a good source the resu l t sare ex tremely favourable

,and there i s produced

in thi s way almost always an improvemen t in thebutter.The u se o f pure cu ltu res i s sti l l qu i te n ew

,

part icu larly in thi s co untry . In the Eu ropeanbutter - making countries they have been used fo ra longer period and have become very much better known . What the fu tu re may develop alongth i s l in e i t i s di fficu l t to say ; but i t seems at

l east p robable that as the di fficu l ties i n the detai l s are mastered the time wi l l come when starters wil l be u sed by our but ter makers for their


cream ripening, j u st as yeast i s u sed by hou sewives fo r raising bread

,or by brewers for fer

men ting mal t. These starters wi l l probably int ime be furn ished by bacteriologists . Bacterio logy

,in other words

,i s offering in the near fu tu re

to ou r butte r makers a method of co ntro l l i ng theripening of the creami n such a way as to insu rethe o o b tain ing of a high and un iform qual i ty o fbu tter

,so far

,at least

,as concern s flavour and

aroma .

BAC T ERIA IN C HEESE .

C /teese ”petting—The th ird great product ofthe dai ry industry i s cheese

,and in connection

with th is product the dai ryman i s even more ‘dependen t upon bacteria than he is i n the production of bu tter. I n the manufactu re o f cheese thecasein o f the mi lk i s separated from the otherproducts by the use of rennet

,and is co l lected

in large masses and pressed,fo rming the fresh

cheese . This cheese i s then set aside for several weeks

,and sometimes for months, to under

go a process that i s known as r ipen ing. Duringthe ri pening there are developed i n the cheese thepecu l iar flavo urs which are characteri st ic of thecompleted product . The taste of freshly madecheese i s extremely un like that of the ri penedproduct . Whi le butter made from unripenedcream has a pleasan t flavou r

,and one which i s

in many places particu larly enjoyed , there i s nowhere a demand fo r un ripened cheese, fo r thefresh ly made cheese has a taste that scarce anyone regards aspl .easant Indeed , the whole valueo f the cheese is dependent upon the flavour o fthe product

,and this flavour 18 developed during

the ripen ing.

REL AT ION OF BAC T ERIA T O DAIRY INDUST RY. 8 7

The cheese maker finds in the ripen ing of hi scheese the most difficu l t part o f his manufactu re .

I t i s indeed a process over which he has veryl i ttl e contro l . Even when al l conditions seemtobe correct

,when cheese i s made in the most care

fu l manner , i t no t i nfrequen tly occurs that theripen i ng takes place in a mann er that i s en ti rely abnormal , and the resu l ting cheese becomesworth less . The cheese maker has been at an en

t i re loss to understand these i rregu lari ties,n O I

has he possessed any means of removing themT he abnormal r ipeni ng that occurs takes on various types . Sometimes the cheese wi l l becomeextraordinar i ly porous

,fi l led with large ho les

which cause the cheese to swel l o u t of propershape and become worthless. At o ther timesvario us spots o f red or blue appear i n the manufactured cheese ; whi le again unpleasant tastesand flavours develop which render the product o fno val ue . Sometimes a considerable portion ofthe product o f the cheese facto ry undergoes suchi rregu lar ripening

,and the product for a long

time wi l l thus be worth less . I f some meanscou ld be discovered o f removing these irregularities i t wou ld be a great boon to the cheesemanufactu rer ; and very many attempts havebeen made in one way or another to furn ish thecheese maker with some detai l s i n the man ufacture which wi l l enable him i n a measure to control the ripening.

The ripening o f the cheese has been subj ectedto a large amount of study on the part o f bacterio lo gists who have been in terested in dai ryproducts . That the ripen ing of cheese i s theresu l t of bacteria l growth therein appears to beprobable from a prio ri grou nds . Like the ri pen


ing of cream ,i t i s a process that occu rs some

what slowly . It i s a chemical change which i saccompanied by the destruction of pro teid matter ; i t takes place best at certain temperatu res,and temperatu res which we know are favourableto the growth o f micro - organ isms

,al l of which

phenomena suggest to us the action of bacteria .

Moreover,the flavours and the tastes that ari se

have a decided resemblance i n many cases to thedecomposit ion products of bacteria

,strikingly so

i n Limbu rger cheese . When we come to studythe matter o f cheese ripening carefu l ly we learnbeyond question that this a prio ri concl u sion iscorrect . The ripen ing of any cheese i s dependen t upon several di fferent factors . The methodof preparation

,the amount of water left i n the

cu rd,the temperatu re of ripen ing

,and other mis

cellaneo us facto rs connected wi th the mechan icalprocess of cheese manu factu re, affect i ts character. Bu t

,i n addi tion to al l these factors

,there i s

undoubtedly another one, and that i s the numberand the character of the bacteri a that chance tobe in the curd when the cheese i s made . Whil e i ti s fou nd that cheeses which are treated by differen tprocesses wi l l ri pen in a di fferen t manner

,i t i s a l so

found that two cheeses which have been madeunder simi la r conditions and treated i n identical l ythe same way may also ripen in a di fferen t manner

,

so that the resu lting flavour wi l l vary . The variation s between cheeses thus made may be sl ightor they may be considerable

,but variation s cer

tain ly do occur. Every one knows the great di fference i n flavours o f di fferent cheeses

,and these

flavours are due in considerable measu re to facto rs o ther than the simple mechanical process o fmaking the cheese . The general simi lar i ty o f


the whole process to a bacterial fermentationleads u s to bel ieve at the outset that some ofthe differences in character are due to differentkinds of bacteria that mu l tip ly i n the cheese andproduce decomposi tion therein .

When the matter comes to be studied by bacterio lo gy , the demonstration of th is posi tion be

comes easy. That the ripening of cheese is duet o growth o f bacteria i s very easi ly proved bymanufacturing cheeses from mi lk which is de

prived o f bacteria . For in stance , cheeses havebeen made from mi lk that has been ei ther steriliz ed or pasteuri zed—which processes destroymost of the bacteria therein—and

,treated other

wise in a normal manner, are set aside to ripen .

These cheeses do no t ripen,but remain for mo n ths

w ith practical ly the same taste that they hadoriginal ly . In other experiments the cheese hasbeen treated with a smal l amount o f disin fective

,

which is Su fficien t to prevent bacteria from growing

,and again ripen ing is found to be absolutely

prevented . Furthermore,i f the cheese under o r

dinary condi tion s i s studied du ring the ripening

process, i t i s found that bacteria are growing during the who le t ime . These facts al l taken together plain ly prove that the r ipening o f cheesei s a fermentatio n due to bacteria . It wi ll benoticed

,however

,that the conditions in the

cheese are not favou rabl e for very rapid bacterial growth . I t i s true that there is plentyof food in the cheese for bacteria l l i fe

,but the

cheese i s not very moist ; i t i s ex tremely dense,being subj ected i n al l cases to more o r less pressure . The penetration of oxygen in to the centreof the mass must be extremely sl ight. The densi ty

,the lack of a great amount of moi stu re

,and

go T HE ST ORY OF GERM L IFE.

the lack o f oxygen furn ish condition s i n whichbacteria wi l l no t grow v ery rapidly . The conditio ns are far less favou rable than those of ripening cream

,and the bacter ia do no t grow with

anyth ing l ike the rapidity that they grow in

cream . I ndeed,the growth of these o rgan isms

during the r ipening i s extremely slow comparedto the possibi l i ti es of bacterial growth that wehave already noticed . Nevertheless

,the bacteria

do mul tiply in the cheese,and as the ripening

goes on they become more and more abundant,

al though the number fluctuates,ri sing and fal l ing

under differen t conditions.When the attempt i s made to determine the

relatio n of the di fferen t k inds o f ripening to di ffereat k inds o f bacteria

,i t has thu s far met with

extremely l i tt le success. That differen t flavoursare du e to the ripening produced by differen tkinds of bacteria wou ld appear to be almost certain when we remember

,as we have already n o

t iced,the di ff eren t k inds of decomposit io n pro

duced by di fferen t species of bacteria. It wou ldseem

,moreover

,that i t ought n o t to be very diffi

cu l t to separate f rom the ripened cheese the bacteria which are present , and thus obtain the kindof bacter ia necessary to produce the desi red ripening. Bu t fo r some reason thi s does n o t prove t obe so easy in practice as i t seems to be in theory .

Many di ff eren t species of bacteria have been separated from cheeses . One bacterio logist, studyingseveral cheeses

, separated about eighty differen tspecies therefrom

,and others have found perhaps

as many more from differen t sou rces . Moreover

,experimen ts have been made with a co nsid

erable number of these di fferent kinds of bacteriato determine whether they are capable of produc


demonstrate beyond peradventure that the ah

normal ripening o f cheese i s due primari ly to the

growth of improper species therein . Q u i te a longl ist o f species of bacteria which produce abnormal

r ipening have been i so latedfrom cheeses

,and have

been studied and experi

men ted w i th by bacterio lo

0 'gists . As a resu l t of thi sstudy o f abnormal ripening

,

there has been suggested amethod o f partial ly con

Fro . 24.—Dairy bacterium t ro l ling these— remedy ing

gOdudng

“swelled” them The method con

eese .

SIStS s1mply In test Ing thefermenting qual i ties of the milk u sed . A smal lsample of mi lk from diff eren t dairies i s al lowed tostand in the cheese factory by i tse l f unti l i t un

dergo es i ts no rmal sou ring. I f the fermentationor souring that thus occurs i s o f a normal character

,the mi lk i s regarded as proper fo r cheese

making. But i f the fermentation that occurs i nany particu lar sample o f milk i s unusual ; i f anextraordinary amount o f gas bubbles are produced

,or i f u npleasan t smel l s and tastes arise ,

the sample i s regarded as unfavou rable for cheesemaking

,and as l ikely to produce abnormal ripen

ing in the cheeses . Mi lk from thi s source wou ldtherefo re be excluded from ‘the mi lk that i s to beused in cheese making. This

,of course , i s a ten

tative and an unsatisfacto ry method of con tro ll ing the ripen i ng

,and yet i t i s one of some prae

t ical value to cheese makers . I t i s the on lymethod that has y e t been suggested of controll i ng the ri pen ing .

Our bacterio logists,of cou rse

,are qui te con

REL AT ION OF BAC T ERIA T O DAIRY INDUST RY . 93

fiden t that in the future more practical resu l tswi l l be obtained along thi s l ine than in the past .If i t i s tru e that cheeses are ri pened by bacteria ;i f i t i s true that d i ffe rent qual it ies i n the cheeseare due to the growth o f di fferent species of bacteria during the ripen ing, i t wou ld seem to bepossible to obtain the proper kind o f bacteriaand to furnish them to the cheese maker for artificially i nocu lating hi s cheese, j u st as i t has beenpossible to furn ish artificial ly cu l ti vated yeasts tothe brewer

,and as it has become possible to fu r

n ish artificial ly cul tivated bacteria to the bu ttermaker. We must

,however

,recognise thi s to b e

a matter for the futu re . Up to the present timen o practica l resu l ts along the l ines of bacter iahave been obtain ed which our cheese man u fact urers can make use of in the way of con tro l l ingwith any accuracy this process of cheese ripening .

Thus i t wi l l be seen that in thi s last dai ryproduct bacteria p lay even a more important partthan i n any of the o thers . The food val u e o fcheese is dependent upon the casein which is present . The market price

,however

,i s con tro l led

enti rely by the flavour,and th i s flavour is a prod

uct of bacterial growth . Upon the action ofbacteria

,then

,the cheese maker i s absol utely de

pendent ; and when our bacterio logists are able inthe fu ture to investigate this matter further

,i t

seems to be at least possible that they may obtainsome means of enabl ing the cheese maker to co n

t ro l the ripen ing accu rately . Not on ly so,bu t

recogni sing the great variety in the flavours ofcheese , and recognising that di fferen t kinds ofbacteri a undoubtedly produce di ff eren t kinds ofdecomposi tio n products, i t seems to be at leastpossib le that a time wi l l come when the cheese


maker wi l l be ab l e to produce at wi l l any partienlarly desi red flavou r in his cheese by the additionto i t o f particu lar species of bacteria

,or particular

mixtures of species of bacteria which have beendiscovered to produce the desi red effects.

CHAPTER IV.

BAC T ERIA IN NAT URAL PRO C ESSES.

AG RIC U L T URE .

THUS far , i n con sideri ng the relation s of bacteria to mankind

,we have taken into account on ly

the arts and manufact ures,and have found bac

teria playing no unimportant part in many of theindustries o f ou r modern civi l i zed l i fe . So impo rtant are they that there i s no one who is notdIrectly affected by them . There is hardly a moment i n our l i fe when we are no t using some ofthe direct o r indirect products of bacterial action .

We turn n o w,however

,to the consideration o f a

matter of even more fundamen tal importance ;for when we come to study bacteria i n Natu re

,

we find that there are certain natu ral processesconnected with the l i fe o f an imals and plan ts thatare fundamental ly based upon thei r powers . Living Natu re appears l imi t less

,fo r l i fe processes

have been going on in the world through countl ess centu ries with seemingly unimpaired vigou r.At the very bottom we find th i s never - ending exhibitio n of v i tal power dependen t upon certainacti vi ties o f micro - o rgani sms . So thoroughly i sthi s true that

,as we shal l find after a short con

sideration,the continuance of l i fe upon the surface

BAC T ERIA IN NATURAL PRO C ESSES. 95

o f the world wou ld be impossib le i f bacterialaction were checked for any considerable lengthof time. The l ife of the globe i s, in sho rt, dependent upon these micro - o rgan isms.

BAC T ERIA AS SC AVENG ERS .

In the first place,we may notice the value o f

these organisms simply as scavengers,keeping

the surface o f the ear th in the proper conditionfo r the growth o f an imal s and plants. A largetree in the forest dies and fall s to the ground .

For a whi le the tree tru nk l ies there a massi vestructu re

,but in the cou rse of months a slow

change takes place in i t . The bark becomes softened and fal l s from the wood . The wood alsobecomes more or less so ftened ; i t i s preyed uponthen by in sect l i fe ; i ts den si ty decreases moreand more

,un ti l final ly i t crumbles into a soft

,

brown ish, po wdery mass, and eventual ly the

whole sinks into the so i l,i s overgrown by mosses

and other vegetation,and the tree trunk has dis

appeared from view . In the same way the bodyo f the dead an imal u ndergoes the process of thesoften ing of i ts ti ssues by decay. The softerparts of the body rapidly dissipate

,and even the

bones themsel ves even tual ly are covered with thesoi l and disintegrated, unti l in time they, too , disappear from any visible existence. This wholeprocess i s one o f decay

,and the result i s that

the so l id mass of the body of the tree or o f thean imal has been decomposed . What has becomeo f i t ? The answer ho lds the secret of Nature ’seternal freshness . Part of i t has dissipated in tothe air in the form of gases and water vapour ;part o f i t has changed i ts composit ion and has


become i ncorporated in to the soi l,the final result

being that the body o f the plan t or animal disappears as such

,and i ts substance is converted in to

gaseous form, wh ich is dissipated in the ai r o r into

simple compounds which si nk into the earth .

Thi s who le process o f decay of organi c l i fe i sone in which bacteria play the most impo rtan tpart . In the case of the decomposition o f thewoody matter of the tree trunk

,the process i s be

gun by the agency of mou lds,for this group of

organ isms alone appears to be capable of attacking such hard woody structu re . The later parto f the decay

,however

,i s largely carried on by

bacterial l i fe. I n the decomposition o f the animal t i ssues

,bacteria alone are the agents. Thus

the process by which o rgani c matter i s di ssipatedin to the ai r or i ncorporated into the soi l i s onewhich i s primari ly presided over by bacteriall i fe .

Viewing this matter in a purely mechanicall ight

,the importance of bacteria i n thu s acting as

scavengers can hardly be overestimated . I f wethink for a moment o f the condi tion of the worldwere there no such decomposing agents to rid theearth ’s surface o f the dead bodies of animal s andplants

,we shal l see that long since the earth

wou ld have been uninhabitable I f the deadbodies of plan ts and animal s of past ages simplyaccumu lated on the surface of the ground without any forces to reduce them into simple compounds for dissipation

,by thei r very bu lk they

wou ld have long since completely covered thesu rface of the earth so as to aff ord no possibleroom for fu rther growth of plants and animals .I n a pu rely mechan ica l way

,then

,bacteria as de

composition agents are necessary to keep the sur

BAC T ERrA IN NAT URAL PROC ESSES. 97

face of the earth fresh and unencumbered so thatl i fe can conti nue .

BAC T ERIA AS AG ENT S IN NAT URE’

S FO OD

C YC L E .

But the matter by no means ends here . Whenwe come to think of i t, i t i s a matter of con siderable surpri se that the surface o f the earth hasbeen able to contin u e producing animals andp lants fo r the many mi l l ions of years duringwhich l i fe has been i n ex istence . Plants and an imals both requ i re food

,animals depending whol ly

upon plants therefor . Plan ts, however, equal lywith animals

,requi re food

,and although they Oh

tain a considerable portion of thei r food from theair

,yet no inconsiderable part o f i t is obtained

from the soi l . The question is fo rced upon u s,

therefore,as to why the soi l has no t long since

become exhau sted of food . How could the soi lcon tinue to support plants year after year formi l l ion s of years

,and y e t remain as ferti l e as

ever ?The explanation o f thi s phenomenon i s in the

simple fact that the processes of Nature are suchthat the same food is used over and over again

,

fi rst by the plan t,then by the animal, and then

agai n by the plant, and there i s no necessi ty fo rany end of the process so long as the sun fu rn ishes energy to keep the ci rcu lation contin uous .One phase o f thIS transference of food fromanimal to plan t and from plant to an imal i sfami li ar to nearly every one . I t i s a wel l - knownfact that animals in thei r respiratio n consumeoxygen

,bu t exhale i t again in combination with

carbon as carbon ic diox ide . On the other hand,

7

T HE ST ORY O F G ERM L IFE .

plan ts in thei r l i fe consume the carbon ic dioxideand exhale the oxygen again as free oxygen .

Thus each o f these kingdoms makes use of theexcreted product of the other

,and this process

can go on indefini tely,the an imal s fu rnish ing ou r

atmosphere wi th plen ty of carbonic acid for plan tl i fe

,and the plan ts excreting into the atmosphere

at the same time an abundan t su fficiency of oxygen for animal l i fe . The oxygen thu s passes inan endless ro und from animal to p lan t and fromplan t to animal .A similar cycl e i s true o f al l the other foods

of an imal and plan t l i fe,tho ugh in regard to the

o thers the operation is more complex and moremembers are requ i red to complete the chain .

The transference of matter through a series o fchanges by which i t i s brought from a condi tionin which i t i s proper food fo r plan ts back againin to a condition when i t i s once more a properfood for plants

,i s one o f the in teresting dis

co veries of modern science,and one in wh ich

,as

we Shal l see,bacteria p lay a mo st important part .

This food cycle i s i l lu strated roughl y by the

accompanying diagram ; but in order to understand it

,an explanation of the various steps in

this cycle is n ecessary .

I t wi l l be noticed that at the bottom of thecircle represen ted i n Fig . 25 , at A,

are givenvariou s ingredients which are found in the soi land which form plant foods . Plant foods

,as

may be seen there,are obtained part ly from the

ai r as carbonic d iox ide and water ; but anotherportion comes from the soi l . Among the soi lingredients the most prominent are n i trates

,

which are the forms of ni trogen compoundsmost easi ly made use of by plan ts as a sou rce of


of plan t l i fe consist o f such materia ls as sugar,

starches,fats

,and proteids

,al l of which have

been manufactu red by the plan t from the ingredien ts fu rn i shed i t from the soi l and ai r

,and

through the agency of the sun ’s rays . Theseproducts o f plan t l i fe now fo rm foods for the

an imal kingdom . Starches,fats

,and proteids are

an imal foods,and upon such complex bodies

alone can the an imal kingdom be fed . Animall i fe

,standing high up i n the ci rcle , i s not capable

of extracting i ts nu trimen t from the so i l,but must

take the more complex foods which have beenmanufactu red by plan t l i fe . These complexfoods enter now into the animal and take thei rp lace in the animal body . By the an imal act iv ities

,some o f the foods are at once decomposed

i n to carbonic acid and water,which , being dis

sipated i n to the ai r, are brought back at oncei nto the condi tion i n which they can serve againas plan t food . This part o f the food is th u sbrought back again to the bottom of the circle

(Fig. 25 , dotted l ines) . But whi le i t i s true thatanimals do thus reduce some of thei r foods tothe simple condi tion of carbonic acid and water

,

this i s no t true of most of the foods which contain n itrogen . The n i trogenous foods are asnecessary for the l i fe as the carbon foods

,and

animals do n o t reduce thei r n itrogenous foodsto the conditio n in which plants can prey uponthem . Whi le plants fu rn ish them with n itro ge

nous food , they can not give i t back to the p lants.Part o f the n i trogenous foods an imals bu i ld inton ew albumins (Fig. 25 C) ; but a part of them theyreduce at once into a somewhat simpler conditionknown as u rea . Urea i s the form in which theni trogen i s common ly excreted from the animal

BAC T ERIA IN NAT URAL PRO C ESSES. 1 0 1

body . Bu t u rea i s not a p lan t food ; for ordinaryplan ts are enti re ly unable to make use o f i t .Part of the n i trogen eaten by the an imal i s sto redup i n i ts body, and thus the body of the animal,after i t has died

,contain s these n itrogen com

pounds o f high complex ity . Bu t plants are n o table to u se these compounds . A plant can not befed upon muscle t issu e

,nor upon fats

,n o r bones

,

for these are compounds so complex that the simple plant i s unable to u se them at al l . So far

,

then,i n the food cycle_the compounds taken from

the soi l have been bui l t up in to compounds ofgreater andgreater complexi ty ; they have reachedthe top of this ci rcle

,and no part of them

,except

part o f the carbon and oxygen,has b ecome re

duced again to plant food . I n order that thi smaterial shou ld again become capable of entering i n to the l i fe o f plants so as to go over theci rcle again

,i t i s n ecessary for i t to be once

more reduced from its h igh ly complex conditioninto a simpler o n e .

Now come in to play these decomposi tionagencies which we have been studying under thehead of scavengers . I t wi l l be noticed that then ext step in the food cycle i s taken by the decomposi t ion bacteria . These o rgani sms, exi sting

,as we have al ready seen

,i n the ai r

,i n the

soi l,i n the water

,and always ready to seize ho ld

of any organic substance that may fu rni sh themwith food

,feed upon the produ cts o f an imal l i fe

,

whether they are such products as muscle tissue,

or fat,or sugar

,or whether they are the excreted

products o f animal l i fe,such as u rea

,and produce

therein the chemical decomposi tio n changes al

ready noticed . As a resu l t o f this chemicaldecomposit ion

,the complex bodies are broken

1 0 2 T HE ST ORY OF GERM L IFE.

i nto simpler and simpler compounds, and thefinal resu l t i s a very tho rough destruction of theanimal body or the material excreted by an imall i fe

,and its reduction in to fo rms simple enough

for plants to u se again as foods . Thus the bacteria come in as a necessary l ink to connect thean imal body, or the excretion from the animalbody

,with the so i l again , and therefore with that

part o f the ci rcle in which the material can oncemore serve as plant food .

But in the decomposi tion that thu s occu rsthrough the agency of the putrefactive bacteriai t very commonly happens that some of the foodmaterial i s broken down into compounds too simple for u se as plant food . As wi l l be seen by aglance at the diagram (Fig . 25 D) , a portion o f thecleavage products resu lting from the destructionof these an imal foods takes the fo rm of carbonicacid gas and water These ingredien ts are ato n ce in condition for plant l i fe

,as shown by the

dotted l ines . They pass o ff in to the ai r,and the

green leaves of vege tat IO n everywhere againseize them, assimi late them ,

and use them asfood. Thus i t is that the carbon and the oxygenhave completed the cycle

,and have come back

again to the po si tion i n the ci rcl e where theystarted . I n regard to the n i trogen portion of thefood

,however, i t very common ly happens that the

products which arise as the resu l t o f the decomposit io n processes are n o t yet in proper condi tionfor p lan t food . They are reduced into a conditionactual ly too simple for the u se o f plants . As aresu l t of these putrefactive changes

,the n itrogen

products o f animal l i fe are broken frequen tlyin to compounds as simple as ammon ia (NFL ) , orinto compounds which the chemi sts speak o f as


means of which the ammonia is uni ted with oxy.

gen and bu i l t up into a serie s of products final lyresu lting in n itrates (Fig . By the action ofother species sti l l higher n i trogen compounds

,in

cl uding the ni tri tes, are fu rther oxidized and bu i l tup into the form of n i trate s . Thus these ni tri fying organisms fo rm the last l ink in the chain thatbinds the an imal k ingdom to the vegetable kingdom (Fig . 25 at For after the n i tr ifying o r

gan isms have oxidized ni trogen cleavage products,the resu l ts o f the ox idation in the form of ni tratesor n i tric acid are left i n the so i l

,and may now be

seized upon by the roo ts of p lants,and begin once

more thei r j ourney around the food cycle . In thi sway i t wi l l be seen that whi le p lan ts

,by bui lding

up compounds,form the connecting li nk between

the soi l and animal l i fe,bacteria in the other hal f

o f the cycle,by reducing them again

,give u s the

connecting l ink between animal l i fe and the soi l .The food cycle wou ld be as incomplete withou tthe agency of bacteri al l i fe as it wou ld be withou t the agency of plant l i fe.

But even yet the food cycle i s not complete .

Some of the processes of decomposi t io n appearto cau se a portion of the n itrogen to fly ou t o fthe circle at a tangent . In the process o f decomposi tion which is going o u through theagency o f micro - organ i sms

,a considerable part

of the n i trogen i s dissipated into the ai r in theform of free n i trogen . When a bi t of mea t decays

,part o f the meat i s

,indeed

,converted in to

ammonia o r other ni trogen compounds,but i f the

pu trefaction i s al lowed to go on,in the end a

con siderable portion of i t wi l l be broken intost i l l simpler forms

,and the n i trogen wi l l final ly be

dissipated into the air i n the form of free n itro

BAC T ERIA IN NAT URAL PRO C ESSES.

gen . This dissipation o f free ni trogen in to theair i s going on in the world wherever putrefactiontakes place . Wherever decomposition of n i trogenproducts occu rs some free n i trogen i s el iminated .

Now,thi s part of the n i trogen has passed beyond

the reach of p lan ts,fo r p lan ts can not extract

free ni trogen from the ai r . In the diagram this i srepresented as a portion of the materia l which

,

through the agency of the decomposi tion bacteria, has be en thrown ou t o f the cycle at a tangent (Fig . 25 E) . I t wi l l

,o f cou rse

,be plain

from this that the store of ni trogen food must beconstantly dimini shing. The so i l may have beenoriginal ly suppl ied with a given quanti ty of n i trogen compound

,bu t if the decomposi tion products

are causing considerable quantitie s of thi s n i trogen to be dissipated in the ai r

,i t p lain ly fol lows

that the total amount o f n i trogen food uponwhich the an imal and vegetable kingdoms candepend is becoming constantly reduced by suchdissi pation .

There are sti l l o ther methods by which n i t rogen i s being lo st from the food cycle . First

,we

may notice that the ordinary processes o f vegetation resu l t in a gradua l drain ing o f the soi l anda throwing o f i ts n i trogen into the ocean . Thebody of any animal or any plant that chances tofal l into a brook or r iver i s even tual ly carried tothe sea

,and the products of i ts decomposi tion

pass in to the ocean and are,of course

,lost to the

soi l . Now,whi le thi s gradual extractio n of n i

trogen from the soi l by drainage is a slow one,i t

i s neverthe less a su re one . I t i s far more rapidin these years of civi l i zed l i fe than in formertimes

,since the products o f the so i l are given to

the C i ty,and then are thrown into i ts sewage .

1 06 T HE ST ORY O F GERM L IFE.

Our cities,then

,with our presen t system of dis

posing of sewage,are draining from the soi l the

ni trogen compounds and throwing them away .

I n yet another di rection must i t be noti cedthat ou r n i trogen compounds are being lost toplant l i fe—v iz . , by the u se of various n i trogencompounds to fo rm explosives . G unpowder

,n i

tro - glycerine,dynamite

,i n fact . nearly al l the ex

plosives that are used the world over fo r al l so rtsof purposes

,are nitrogen compounds . When they

are exploded the n i trogen of the compound isdissipated into the ai r i n the formof gas

,much

of i t i n the form of free n i trogen . The basi sfrom which explosi ve compounds are made co ntain s ni trogen i n the form in which it can be usedby plan ts . Sal tpetre , for example, i s equal lygood as a ferti l i zer and as a basi s for gunpowder.The products o f the explosion are gases n o

longer capable o f use by plants,and thus every

explosion o f n i trogen compounds aids in thi sgradual di ssipation of ni trogen products

,taking

them from the store of p lant foods and throwingthem away .

Al l of these agencies contribute to reduce theamount of materia l ci rcu lating in the food cycleof Natu re

,and thus seem to tend inevitably in

the end toward a termin ation o f the processes ofl i fe ; for as soon as the soi l becomes exhausted o fi ts ni trogen compounds

,so soon wi l l plant li fe

cease from lack o f nutri t ion,and the di sappear

ance of animal li fe wi l l fol low rapid ly . I t i s thi sloss of n i trogen i n large measu re that is forcingour agricu l turists to purchase ferti l i zers . Thelast fi fteen years have shown us

,however

,that

here again we may look upon our fr iends, thebacteria

,as agents fo r counterac ting this d issi


of the free n i trogen of the atmosphere . I t wasfound

,however, some fifteen years ago that some

species o f p lan ts,chiefly the great fami ly of

legumes,which contains the pea plant

,the bean

,

the clover,etc . ,

are able,when growing in so i l

that is poor in n i trogen,to obtain n i trogen from

some source o ther than the soi l in which theygrow . A pea plant i n so i l that con tains no n i t ro

gen products and watered with water that contains no ni trogen

,wi l l

,after sprouting and growing

fo r a length of t ime,be found to have accumu

lated a considerable quan tity of fixed ni trogen i nits tissues . The on ly so u rce of thi s n i t rogen hasbeen ev idently from the ai r which bathes theleaves of the plan t or permeates the soi l and

bathes i ts roots. This factwas at first dispu ted

,bu t sub

sequently demon strated to betrue

,and was fo und later to

Ibe associated with the comblued action of these legumesand certain soi l bacteria .

When a legume thu s gains

Fm. 27 .— So il bactefia

n itrogen from the ai r,i t de

which pro duce tu velo ps upon its roots l i tt le

$123

3“the ro o ts bunches known as root nodes'

u les or root tubercles . Thenodules are sometimes the size of the head of apin

,and sometimes much larger than this

,occa

sio nally reaching the size o f a large pea, or evenlarger Upon microscopic examinatio n theyare found to be li tt le nests of bacteria . I n someway the soi l o rgan isms (Fig. 2 7) make thei r wayinto the roots of the sprout i ng p lant

,and find

ing there congen ial env i ronment,develop in con

siderab le quanti ties and produce root tubercles

BAC T ERIA IN NATURAL PRO C ESSES.

in the root . Now,by some enti rely u nknown

pro cess,the legume and the bacteria growing to

gether succeed i n extracting the ni trogen fromthe atmosphere which permeates the soi l

,and fix

ing this n i trogen in the tubercles and the roots i nthe formof n i trogen compounds . The resu l t i sthat

,after a proper period of growth

,the amount

of fixed ni trogen in the plan t is found to havevery decidedly increased (Fig. 25 E ) .This

,of co u rse

,fu rn ishes a starting poin t fo r

the reclaiming of the lost atmospheric n i tro gen .

The legume continues to l i ve i ts u sual l i fe,per

haps increasing the store of n itrogen in i ts rootsand stems and leaves during the whol e of i tsnormal growth . Subsequent ly

,after having fin

ished i ts ordinary l i fe,the plan t wi l l die

,and then

the roots and stems and leaves,fal l ing upon the

ground and becoming bu ried,wi l l be sei zed upon

by the decomposition bacteria already ment io n ed. The n i trogen which has thus becomefixed in thei r t i ssues wi l l undergo the destructivechanges al ready described . This wi l l resu l teventual ly i n the production of n i trates . Thussome of the lo st n i trogen i s restored again to thesoi l in the form of n itrates

,and may now start

on i ts rou te once more around the cycle o f food .

I t wi l l be seen,then

,that the food cycle is a

complete one. Beginn ing with the mineral in

gredien ts i n the soi l , the food matter may starton i ts circu lation from the soi l to the plan t

,from

the plant to the an imal , from the animal to thebacteri um

,and from the bacterium through a

series of o ther bacteria back again to the soi l inthe condition in which i t started. I f

,perchance

,

i n this progress around the ci rcle some of theni trogen i s thrown o ff at a tangent

,this

,too

,


i s bro ught back again to the ci rcl e throughthe agency of bacteria l l i fe . And so the foodmaterial o f animals and p lants con tinues in th i snever - ceasing ci rculation . I t i s the sun l ight thatfurn ishes the energy fo r the motion . I t i s thesu n l ight that forces the food around the ci rcleand keeps up the endless change ; and so long asthe sun continu es to Shine upon the earth the reseems to be no reason why the process shou ldever cease . I t i s th is repeated ci rcu lation thathasmade the contin uation of l i fe possib le fo r themi l l ions and mi l l ions of years of the earth ’s h istory . I t i s th is continued circu lation that makesl i fe possibl e st i l l

,and i t i s on ly th is fact that the

food is thus capable of ever circu lating from an i

mal to plant and from plant to an imal that makesi t possible for the l i vi ng world to conti nu e i tsexistence . But, as we have seen, one half o f thisgreat ci rcle of food change is dependen t uponbacter ial l i fe . Withou t the bacteria l l i fe the animal body and the anima l excretion co u ld neverbe brought back again wi thin the reach of the

plan t ;a and thus, were i t n o t fo r the action o f

these micro - organi sms the food cycle wou ld beincomplete and l ife cou ld not con ti nue indefin itely upon the su rface of the earth . At thevery foundation , the continuation of the presen tcondi tion of Natu re and the ex istence of l i feduring the past hi s tory of the world has beenfundamental ly based upon the ubiqui tous presence of bacteria and upon thei r con tin ual actionin connection with both destructive and constructive processes.

1 1 2 T HE ST ORY OF G ERM L IFE .

seed . I t has been claimed that thei r growth tendsto soften the food material in the seed

,so that

the young seedl ing can more readi ly absorb i t fori ts own food

,and that withou t such a soften ing

the seed remains too hard fo r the p lan t to use .

This may wel l be doubted,however

,for seeds

can apparently Sprout wel l enough without theaid of bacteria . But

,nevertheless

,bacteria do

grow i n the seed during its germination , and thusdo aid the plant i n the soften ing o f the food material. We can not regard them as essential toseed germination . I t may wel l be claimed thatthey o rdinari ly play at least an in cidental part i nth is fundamental l i fe process

,although it i s un

certain whether the growth of seed lings i s to anyconsiderable exten t aided thereby .

T HE SI L O .

In the management of a si lo the farmer hasundoub tedly another great bacterio logical probl em. In the attempt to preserve his summergrown food fo r the winter use o f hi s an imals,he i s hindered by the activi ty of commo n bacteria . If the food i s kept moist

,i t i s su re t o

un dergo decomposition and be ru ined in a shortt ime as animal food . T he farmer finds i t n eces

sary,therefore

,to dry some kinds of foods

,l ike

hay . Whi le he can thus preserve some foods,others can not be so treated . Much of the ran kgrowth of the farm

,l ike cornstalks

,i s good food

whi le i t i s fresh,but i s of l i ttle value when dried .

The farmer has from experience and observatio ndiscovered a method of managing bacterialgrowth which enables him to avoid thei r ordinaryevi l effects . This is by the use of the si lo . T he

BAC T ERIA IN NAT URAL PRO C ESSES .

si lo i s a large,heavi ly bui l t box

,which is open

only at the top . In the si lo the green food ispacked tightly

,and when fu l l all access o f ai r i s

excl uded,except at i ts su rface . Under these

condi tions the food remain s moi st, but n everthe

less does n o t undergo i ts ordinary fermentation sand putrefactions, and may be preserved formonths withou t being ru ined . The food in sucha si lo may be taken out months after i t i s packed

,

and wil l sti l l be found to be in good condition fo Ifood . I t i s tru e that

'

i t has changed i ts charac~ter somewhat , but i t i s not decayed, and is eagerlyeaten by catt le .

We are yet very ignoran t of the natu re of thechanges which occur in the food whi le in the si lo .

The food is no t preserved from fermen tation .

When the si lo is packed slowly,a very decided

fermentation occu rs by which the mass is raisedto a high temperatu re (1 40

° F . to 1 60° F ) .

This heating is produced by certain species o fbacteri a which grow readi ly even at thi s hightemperature . The fermentation uses up the ai ri n the si lo to a certai n extent and produ ces asett l i ng of the material which sti l l fu rther excludes ai r . The fi rst fermentatio n soon ceases

,

and afterward on ly slow changes occu r . Certainacid - producing bacteria after a l i ttle begin togrow slowly

,and in time the si lage is rendered

somewhat sour by the production o f acetic acid .

Bu t the exclu sion of air,the close packing

,and

the small amount of moistu re appear to preven tthe growth of the common putrefacti ve bacteria

,

and the si lage remain s good for a long time . InO ther methods o f fi l l ing the si lo

,the food is very

qu ickly packed and densely crowded together soas to excl ude as much ai r as possible from the

8

I I4 T HE ST ORY O F GERM L IFE.

beginning Under these condi tion s the lack ofmoisture and ai r prevents fermen tative actionvery largely . On ly certain acid - producing organisms grow

,and these very slowly . The essen tia l

resu l t in ei ther case is that the common putrefact ive bacteria are prevented from growing, probably by lack of su fficien t oxygen and mo istu re

,

and thus the decay is preven ted . The closelypacked food offers j u st the same unfavou rablecondi tion fo r the growth of common pu trefactivebacteria that we have al ready seen o ffered by thehard - pressed cheese

,and the bacteria growth is

in the same way held in check . Our knowledgeo f the matter i s as yet very sl ight, bu t we doknow enough to u nderstand that the successfu lmanagement of a si lo i s dependen t upon themanipu lation of bacteria .

T HE FERT I L IT Y O F T HE SO I L .

The farmer 's so l e du ty is to ex tract foodfrom the so i l . This he does ei ther di rectly byraisi ng crops

,or i nd irect ly by rai sing an imal s

which feed upon the products o f the soi l . Ineither case the fert i l i ty o f the so i l i s the fundamental factor in hi s success. This ferti l i ty is agi ft to him from the bacteria.

Even in the first fo rmatio n of so il he i s in ameasure dependen t upon bacteri a . Soi l

,as i s we l l

known,i s produced in large part by the crum

bling of the rocks in to powder. Th 1s crumblingwe general ly cal l weathering, and regard It as dueto the effect of moistu re and cold upon the rocks

,

together wi th the o x idi z ing action of the ai r .Doubtless th i s is true, and the weathering actioni s largely a physical and chemical one . Never

1 1 6 T HE ST ORY O F G ERM L IFE .

dien ts has been more or less o f a pu zz le . Ferti lesoi l everywhere contains ni trates and o ther'n itro

gen compounds,and i n certain parts o f the world

there are large accumu lation s of these compounds,

l i ke the ni trate beds of Chi l i . That they have‘

come u l timately from the free atmospheric n it rogen seems certain

,and vario u s attempts have been

made to explain a method of th is n i trogen fixat ion . I t has been suggested that e lectrical di scharges in the ai r may form ni tric acid , whichwou ld readi ly then unite with soi l i ngredients toform n i trates . There i s l i tt l e reason , however,for believing thi s to be a very important factor .Bu t in the so i l bacteria we find undoubtedly aneflicien t agen cy i n this n i trogen fixation . As already seen

,the bacteria are able to sei ze the free

atmospheric nitrogen,converting i t in to n itrites

and n i trates . We have also learned that theycan act in connection with legumes and someother plants

,enabl ing them to fix atmospheric ui

trogen and store i t in thei r roots . By these twomeans the n i trogen ingredien t i n the so i l i s prev en ted from becoming exhausted by the processesof dissipation constant ly go ing on . Further

,by

some such agency must we imagin e the origi naln i trogen soi l i ngredien t to have been derived .

Such an organic agency is the on ly one yet di scerned which appears to have been eflicien t i nfu rn ish ing vi rgi n so i l wi th i ts n i trates

,and we

must therefore look upon bacteria as essential tothe original ferti l i ty o f the soi l .But in another direction st i l l does the farmer

depend direct ly upon bacteria . The most important facto r i n the ferti l i ty of the soi l i s the partof i t cal led llamas. This humus is very complex

,

and never al ike in di ff erent soi l s . I t contain s n i


t rogen compounds in abundance,together wi th

su lphates,phosphates

,sugar

,and many other sub

stances . I t i s this which makes the garden soi ld i fferent from sand

,or the rich soi l d i fferent from

the steri le so i l . I f the soi l is cu lt ivated year afteryear

,i ts fo o d. ingredien ts are slowly bu t surely

exhau sted . Something i s taken from the humuseach year

,and un less thi s be replaced the so i l

ceases to be able to support l i fe . To keep up aconstant y ie ld from the so i l the farmer understands that he must apply ferti l i zers more or lesscon stantly .

This appl ication of ferti l iz ers i s simply feeding the crops . Some of these fert i l i zers the farmer purchases

,and knows l i tt l e or nothing as t o

their o rigin . The most common method of f eeding the crops is

,however

,by the use of o rdinary

barnyard manure . The reason why thi s materia lco ntains plant food we can understand

,Since i t

i s made of the undigested part of food,together

with al l the u rea and other excretion s of an imals,

and contains,therefore

,besides various min era ls

,

al l o f the n itrogenous waste of animal l i fe . Thesesecretion s are not at fi rs t fi t fo r p lant food . T he

farmer has learned by experience that such ex o retion s

,before they are of any use on hIS fields

,

must undergo a process of slow change,which

is sometimes cal led ripen ing . Fresh manure i ssometimes u sed on the fie lds

, but i t i s on ly madeuse of by the plants after the ripen i ng processhas occurred . Fresh an imal excretion s are O f

l i t tl e o r no value as a ferti l i ze r . The farmer,

therefore,common ly al lows i t to remain in heaps

for some time,and i t undergoes a slow change

,

which gradual ly converts i t i nto a condi tion inwhich i t can be used by plan ts . Thi s ripen ing is


readi ly exp lained by the facts al ready considered.

The fresh animal secretions consi st of variou shigh ly complex compounds o f n i trogen , and theripen ing is a process of thei r decomposit ion . The

proteids are broken to pieces, and thei r n itrogenelements reduced to the form of n i trates

,l eucin

,

etc .,or even to ammonia or free n i trogen . Fur

ther , a second process occu rs, the process ofoxidation of these ni trogen compounds al readynoti ced

,and the ammo n ia and ni tri tes resu l ting

f rom the decomposi tion are bu i lt i n to n itrates .I n short

,i n thi s ripen ing manu re the processes

not iced in the fi rst part o f thi s chapter are takingp lace

,by which the complex n i trogenous bodies

are first reduced and then ox idized to form plan tfood . The ripening of manu re i s both an analy tical and a synthetical process. By the analysi s

,proteids and ot her bodies are broken into very

simple compounds,some of them

,indeed

,being

dissipated into the air,but other port ion s are re

tained and then ox idized , and these latter becomethe real ferti l i z ing material s . Through the agencyof bacteria the compost heap thu s becomes thegreat so u rce of pl an t food to the farmer . Intothi s compost heap he throws garbage

,straw

,v ege

table and an imal substances in general,or any

organ i c refu se which may be at hand . The vario us bacteria sei ze i t al l , and cau se the decomposit ion which converts i t in to plant food again . Therotting of the compost heap is thu s a giganticcu l tivation of bacteria .

Thi s knowledge o f the ripening process i s fu rther teaching the farmer how to preven t waste .

In the ordinary decomposi tion of the compostheap not an inconsiderable portion of the n i trogen i s lost in the ai r by dissipation as ammonia


pate some of the n i t rogen in to the ai r as free n it rogen .

To meet th i s emergency and loss the farmerhas another method of en riching the soi l

,again

depending upon bacte ria . This i s the so - cal led

green manuring . Here certain p lants which seizen i trogen from the ai r are cu lt ivated upon the fieldto be fert i l i zed

,and, i n stead of harvesting a

crop,i t i s p loughed in to the soi l . Or perhaps

the tops may be harvested,the rest being

ploughed into the soi l . The vegetable materia lthus ploughed in l ies over a season and enrichesthe so i l . Here the bacteria of the soi l come intoplay in several directions . First

,i f the crop

sowed be a legume,the so i l bacteria assi st i t to

seize the n i trogen fromthe ai r. The on ly plantswhich are of use in thi s green man uring are thosewhich can

,through the agency o f bacteria

,obtain

n i trogen fromthe ai r and store i t i n thei r roots.Second

,after the crop is plo ughed into the soi l

various decomposing bacteria seize upon it,pu l l ing

the compounds to pieces. The carbon i s largelydi ssipated into the ai r as carbon ic diox ide , wherethe next generation of plan ts can get ho ld of i t .The minerals and the ni trogen remain in the soi l .The ni trogenous portions go through the sameseries of decomposi tion and sy nthetical changesal ready described

,and thus even tual ly the ni tro

gen seized from the ai r by the combined actionof the legumes and the bacteria i s converted in toni trates

,and wi l l serve fo r fo od for the nex t se t

of plants grown on the same soi l . Here i s thus apractical method of u sing the ni trogen assimi lat ion powers of bacteria

,and reclaiming n i trogen

from the ai r to replace that which has been lost .Thus i t i s that the farmer ’s n i trogen prob lem


o f the ferti le soi l appears to reso lve i tse l f i n to aproper handl ing of bacteria . These organismshave stocked his soi l in the fi rst place . Theyconvert al l o f hi s compost heap wastes in to simplebodies

,some of which are changed into plan t

foods,whi le others are at the same time lo st .

Last ly,they may be made to reclaim th i s lost

n i trogen,and the farmer

,so soon as he has

requisi te knowledge o f these facts,wi l l be able

to keep within hi s con tro l the supply of thi s importan t e lement . The continued fer t i l i ty of thesoi l is thus a gift from the bacteria .

BAC T ERIA AS SO URC ES O F T RO UBL E T O T HE

FARMER.

Whi le the topics al ready con sidered comprisethe most impo rtan t factors i n agricu ltu ral bacterio lo gy , the farmer

’s re lation s to bacteria donot end here . These o rganisms come inciden tal lyinto h is l i fe i n many ways . They are not alwayshi s aids as they are in most o f the in stances thusfar C i ted . They produce di sease in hi s cattle

,as

wi l l be noticed in the nex t chapter . Bacteria areagents of decomposi tion

,and they are j ust as

l ikely to decompose materia l which the farmerwishes to prese rve as they are to decompose mat erial which the farmer desires to undergo theprocess o f decay . They are as ready to attackh is fru i ts and vegetables as to ripen h is cream .

The sk1n of fru i ts and vegetables is a moderatelygood pro tection o f the in terio r from the attacko f bacteria ; bu t i f the ski n be broken i n anyplace

,bacteria get i n and cause decay , and to

preven t i t the farme r uses a cold cel lar . Thebacteria preven t the farmer from preserving

1 2 2 T HE ST ORY OF G ERM L IFE .

meats for any length of time un less he checksthei r growth i n some way . They get into theeggs of his fowls and ru in them . Their troublesome nature in the dai ry in preventing the keeping of mi lk has already been n oticed . I f heplan ts hi s seeds i n very moist

,damp weather

,

the soi l bacteria cause too rapid a decomposi tionof the seeds and they ro t i n the ground in steadof sprou ting. They produce di sagreeab l e odou rs

,

and are the cause of most of the pecul iar smel l s,

good and bad,around the barn . They attack

the organic matter which gets in to his wel l orbrook o r pond

,decomposing i t

,fi l l ing the water

with disagreeable and perhaps poisono u s productswhich render i t unfi t to drink . They not on ly aidin the decay of the fal l en tree in his forests

,but

in the same way attack the timber which hewishes to preserve

,especial ly i f i t i s kept in a

moist condition . Thus they contribute largelyto the gradual destruction o f wooden structu res.It i s therefo re the presence o f these organ ismswhich forces him to dry hi s bay , to smoke hi shams

,to corn his beef

,to keep his fru i ts and

vegetables coo l and prevent skin bru ises,to ice

his dairy,to protect h i s timber from rain

,to use

stone in stead of wooden foundations fo r bu i ldings

,etc . I n general

,when the farmer desi res

t o get rid of any o rgan ic refuse,he depends upon

bacteria,for they are his so le agents (aside from

fi re) fo r the final destruction of organ ic matter.When he wishes to convert waste organ ic refusein to ferti l iz i ng materia l

,he u ses the bacteria of

his compost heap . O n the other hand,whenever

he desi res to preserve o rganic material,the

bacteria are the enemies against which he mustcarefu l ly guard .


n o ts of the gas manu factu re . From the coa lal so comes coal tar

,the material from which such

a long series o f val uable materials,as ani l ine

colou rs,carbo l ic acid

,etc .

,i s derived . The l i st of

products which we owe to coal is very long,and

the value of thi s materi al i s hardly to be overrated . In the preparation o f these ingredientsfrom coal bacteria do not play any part . Mostof them are derived by means of disti l lation . But

when asked for the agents wh ich have given u sthe coal of the coal beds

,we shal l find that here,

too,we owe a great debt to bacteria .

Coal,as i s wel l known

,has come from the ao

cumu lat ion of the l ux u rian t vegetable growth ofthe past geologica l ages. It has therefore beendirectly fu rn ished u s by the vegetat ion of thegreen plan ts of the past

,and

,in general

,i t repree

sents so much carbon ic diox ide which theseplants have extracted fromthe atmosphere . Butwhi le the green plan ts have been the activeagents i n producing thi s assimi lation

,bacteria

have played an impo rtant part i n coal manufacture in two di fferent di rect ion s. The fi rst appears to be in furni shing these plan ts wi thn itrogen . Witho ut _a sto re of fixed n i trogen inthe so i l these carbon iferous plants cou ld not havegrown . Thi s matter has already been co nsidered .

We have no very absolute know ledge as to theagen cy of bacteria i n furnishing n i trogen for thi svegetation i n past ages

,but there i s every reason

to bel ieve that in the past,as i n the presen t

,the

chief sou rce of organic n itrogen has been fromthe atmosphere and derived from the atmos

phere th rough the agency of bacteria . In theabsence of any other known factor we may bepretty safe in the assumption that bacteria p layed

BAC T ERIA IN NAT URAL PRO CESSES. 1 25

an importan t part in thi s n i trogen fixat ion,and

that bacteria must therefore be regarded as theagents which have fu rn ished us the n i trogenstored i n the coal .But i n a later stage of coal formation bacteri a

have contributed more direct ly to the formation ofcoal . Coal i s no t simply accumu lated vegetation .

The coal o f ou r coal beds is very di ff erent i n i tschemical composi t ion from the wood of the trees .I t contain s a much higher percentage of carbonand a lower percentage of hydrogen and oxygenthan ordinary vegetable substan ces . The conversion of the vegetation o f the carbon i ferou s agesinto coa l was accompanied by a gradual loss o fhydrogen and a consequent increase in the percentage of carbon . I t is thi s change that hasadded to the density of the substance and makesthe greater value of coal as fuel . There is l i ttl edoubt now as to the method by which this woodymaterial o f the past has been converted into coal .The same process appears to be going on in a

simi lar manner to - day in the peat beds of variousnorthern coun tries . The fal len vegetation

,trees

,

trunks,branches

,and leaves

,accumulate in

masses,and

,when the conditions of moisture and

temperature are right,begin to undergo a fer

mentation . Ordinari ly th is action of bacteria,

as al ready noticed,produces an almost complete

though slow oxidation of the carbon,and resu l ts

i n the to tal decay of the vegetable matter . Buti f the vegetable mass be covered by water andmud under proper conditions of moistu re and tem

perature, a di fferent kind of fermentat ion ari seswh ich does not produce such complete decay .

The covering of water prevents the access o foxygen to the fermenting mass

,an oxidation of


the carbon i s largely preven ted,and the vegetable

matter slowly changes i ts character . Under theinfluence of th i s slow fermentation

,aided

,proba

bly by pressure,the mass becomes more and more

sol id and condensed,i ts woody character becomes

less and less distinct,and there is a gradual loss

of the hydrogen and the oxygen . Doubtlessthere is a loss of carbon also

,fo r there i s an evo

lu t io n of marsh gas which contains carbon . Butin this slow fermentation taking p lace under thewater in peat ho gs and marshes the carbon lossi s relatively smal l ; the woody materia l does n o t

become complete ly ox idized,as it does in free

operations of decay . The loss of hydrogen andoxygen from the mass i s greater than that ofcarbon

,and the percentage of carbon therefore ih

creases . This i s not the ordinary kind of fermentatio n that goes on in vegetable accumu lation s .I t requi res special conditions and possib ly specialkinds of fermenting organisms . Peat i s notfo rmed in al l chmates. I n warm regions

,or

where the woody matter i s freely exposed to theai r

,the fermentation of vegetable matter i s more

complete,and i t i s enti re ly destroyed by ox ida

tion . I t i s o n ly in colder region s and when co v

ered with water that the destruction of the organ icmatter stops short of decay . Bu t such incomplete fermentation i s sti l l going on in many partsof the wo rld

,and by i ts means vegetable ao

cumu lations are being converted into peat .Th1s formation of peat appears to be a first

step in the formation of denser coal . By a cont inuatio n of the same processes the mass becomessti l l more dense and so l id . As we pass from thetop to the bottom of such an accumulation ofpeat

,we find i t becoming den ser and denser

,and

1 28 T HE ST ORY O F G ERM L IFE .

mentation occurri ng i n the v egetat io n thatbrought abou t the chemical changes in It whichresu lted in i ts transformat ion in to coal . The vegetatio n of the carboniferous age was dependen tupon the n i trogen fixed by the bacteria, and tothese o rgan isms also do we owe the fact that thisvegetation was sto red for u s in the rocks.

CHAPTER V.

PARASIT IC BAC T ERIA AND T HEIR REL AT ION T O

D ISEASE .

PERHAPS the most uni versal ly known fact i nregard to bacteria i s that they are the cause o fdisease . I t i s thi s fact that has made them o b

jects of such wide . in terest . This i s the side ofthe subject that fi rst attracted attention

,has been

most studied,and in regard to which there has

been the greatest accumulation o f ev 1dence . So

persi stent ly has the relation of bacteria to di seasebeen di scu ssed and emphasized that the majorityof readers are hard ly abl e to disassociate the two .

To most peop le the very word bacteria i s almostequivalen t to d isease

,and the thought O f swal low

i ng microbes in d rink ing water o r mi lk i s decidedly repugnant and alarming . In the publ ic mindi t i s only necessary to demonstrate that an art ic l eho lds bacteria to throw i t under condemnation .

We have al ready seen that bacteria are to beregarded as agents fo r good

,and that from their

fundamental re lat ion to plant l i fe they must belooked upon as ou r friends rather than as ou renemies . I t i s true that there is another side t o

PARASIT IC BAC T ERIA. 1 29

the sto ry which relates to the parasi tic species .These parasi ti c forms may do u s direct or indirect in j ury . But the species of bacteria which arecapable o f doing u s any in j u ry

,thepat/zogcnic bac

teria,are real ly very few compared to the great

host of species which are harmless . A smal ln umber of species

,perhaps a score or two

,are

pathogenic,whi le a much larger n umber

,amount

ing to hundreds and perhaps thousands o f species,

are perfect ly harmless . This latter class do no inj u ry even though swal lowed by man in thousands .They are not parasi tic

,and are unable to grow in

the body of man . Their presence i s enti rely consi stent wi th the most perfect health

,and

,indeed

,

there are some reasons fo r bel ieving that theyare sometimes di rect ly beneficial to health . I t i senti rel y unj u st to condemn al l bacteria because afew chance to produce mischief. Bacteria in genera l are agents for good rather than i l l .There are

,however

,some species wh ich cause

mankind much trouble by in terfering in o ne wayor another with the normal processes of l i fe .

These pathogenic bacteria,or disease germs

,do

not al l act al ike,but bring abou t inj ury to man in

a n umber of di ffe ren t ways . We may recogn isetwo diff erent classes among them

,which

,how

ever,we shal l see are connected by in termediate

types. These two C lasses are,fi rst

,the patho

genic bacteria,which are no t strictly parasitic bu t

l i ve free in Nature ; and , second , those which l iveas trueparasites i n the bodies of man or othe r an imals . To understand the real relat ion of thesetwo classes

,we must fi rst no tice the method by

which bacteria i n general produce disease.

1 3 0 T HE ST ORY OF G ERM L IFE.

MET HOD BY WH IC H BAC T ERIA PRODUC E

D ISEASE.

Since i t was fi rst clear ly recogn ised that certai n species of bacteria have the power o f prodacing disease, the questio n as to how they doso has ever been a prominent one . Even i f theydo grow in the body

,why shou ld their presence

give ri se to the symptoms character iz ing disease ? Variou s answers to this question havebeen given i n the past . I t has been suggestedthat i n thei r growth they consume the food ofthe body and thu s exhaust i t ; that they producean oxidation o f the body tissues

,or that they

produce a reduction of these ti ssues,or that

they mechan ically in terfere with the circu l ation .

None of these suggestions have proved of muchvalue . Another v iew was early advanced

,and has

stood the test of time . This C laim is that thebacteria whi le growing in the body produce poisons

,and these poisons then have a direct action

on the body . We have al ready noticed that bacteri a during their growth in any medium producea large number of bipro ducts of decomposi tion .

We noticed also that among these bipro ducts

there are some which have a po isonous natu re ;so poisonou s are they that when inocu lated intothe body o f an an imal they may produce poisoning and death . We have on ly to suppose that thepathogenic bacteria

,when growing as parasites in

man,produce such poi sons

,and we have at once

an explan atio n of the method by which they giverise to disease .

Thi s explanation of germ disease i s more thansimple theory . I t has been i n many cases clearlydemonstrated . I t has been found that the bac


The poi sons wi l l be produced in decaying material bu t wi l l seldom be taken in to the humanbody . These po isons

,produced i n the fi rst

stages of putrefaction,are ox idized by fu rther

stages of decomposi tion in to harmless products.But shou ld i t happen that some of these bacteriaobtained a chance to grow vigorously for a whi lein organic products that are subsequent ly swal

lowed as man ’s food,i t i s p la in that evi l resu l ts

might fol low . If such food is swal lowed by manafter the bacteria have produced their poisonou sbodies

,i t wi l l tend to produce an immediate poi

soning of his system . The effect may be suddenand severe i f considerable quan ti ty of the poisonousmater1al i s swal lowed, or sl ight but protractedi f smal l quan ti t ies are repeatedly con sumed i nfood . Such instances are not u ncommon . Wellknown examples are cases of i ce - cream poisoning

,poison ing from eating cheese o r from drink

ing mi lk,or in not a few instances from eating

fish o r meats within which bacteria have hadopportuni ty for growth . I n al l these cases thepoison is swal lowed In quanti ty suflicien t to giverise quick ly to severe symptoms

,sometimes re

sulting fatal ly , and at other t imes passing o ff assoon as the body succeeds in throwing o ff thepoi sons . I n other cases sti l l

,however

,the

amount of poison swal lowed may be very sl igh t,

too sl ight to produce much effect un less the samebe consumed repeated ly . All such troub le maybe attribu ted to fermented or part ly dec

'

ayedfood . I t is di fficu l t to distingu i sh such in stancesfrom others produced in a sl ight ly di fferent way

,

as fo l lows :I t may happen that the bacteria which grow

i n food products continue to grow in the food

PARASIT IC BAC T ERIA. 1 3 3

even afte r i t i s swal lowed and has passed intothe stomach or intestines . This appears particularly true of mi lk bacteri a . Under these conditions the bacteria are not i n any proper senseparasi tic

,since they are simply l i ving in and

feeding upon the same food which they consumeoutside the body

,and are not feeding upon the

tissues of man . The poi sons which they producewi l l conti nue to be developed as long as the bacteria conti nue to grow

,whether in a mi lk pai l o r

a human stomach . If now the poi sons are ah

sorbed by the body,they may produce a mi ld or

severe disease which wi l l be more or less lasting,

continu ing perhaps as long as the same food andthe same bacteria are suppl ied to the individual .The most important disease of th is class appearsto be the dreaded cizo lcra infantum

,so common

among in fants who feed upon cow ’s mi lk in warmweather. I t i s easy t o

’

understand the natu re ofthi s disease when we remember the great numberof bacteri a i n mi lk

,especially in ho t weather

,

and when we remember that the del icate organism o f the infant wi l l be th rown at once intodi sorder by sl ight amounts o f poi son which wou ldhave no appreciab le effect u pon the strongeradu l t . We can easi ly u nderstand

,fu rther

,ho w

the disease readi ly yields to treatment i f carei s taken to steri l i ze the mi lk given to the patient .We do n o t know to - day the exten t of the

troubles which are produced by bacteria o f thi sso rt . They wi l l

,of course

,be chiefly conn ected

wi th ou r food pro ducts, , and common ly , thoughnot always

,wi l l affect the digestive functions . I t

i s probable that many o f the cases o f summerdiarrh o ea are produced by some such cause

,and


i f they could be traced to thei r sou rce wou ld befo und to be produced by bacteri al poisons swallowed with food or drink

,or by simi lar po isons

produced by bacteria growing in such food afteri t i s swal lowed by the indiv idual . In hot weather,when bacteria are so abundant everywhere andgrowing so rapidly

,i t i s imposs ible to avo id such

dangers completely wi thout exerci sing over al lfood a guard which would be decided ly oppressi ve . It i s wel l to bear in mind

,however

,that

the most common and most dangerous source ofsuch poisons i s mi l k or i ts products

,and fo r this

reason one shou ld hesitate to drink mi lk in hotweather un less i t i s ei ther qu i te fresh or has beenbo i led to destroy i ts bacteria .

PA T HO G ENIC BAC T ERIA WH IC H ARE T RUE

PARASIT ES .

This class of pathogenic bacteria includesthose which actual ly invade the body and feedupon i ts ti ssues instead of l iv ing simply uponswal lowed food . I t i s difficu l t

,however

,to draw

any sharp l ine separating the twoclasses . The bacteria which causedip/zt/zcria (Fig.

for in stance,

do n o t real ly in

FIG . 28 .—Diplztlteria bacillus.

vade the.

bOdy .

They grow In thethroat, attached to i ts wal l s, and are confined tothis external location or to the superficial ti ssues

.

This baci l l us i s, i n sho rt , only found in the mou thand th roat, and is practically confined to the so


produces i s the resu l t of the absorption o f thepo ison s secreted in the intestines .I t i s bu t a step from this to the true parasi tes .

Typlzo z’

a’

f co cr, fo r example, i s a disease producedby bacteria which grow in the in testines

,but

which also invade the ti ssuesmore ex tensively than thecholera germs (Fig. Theydo no t invade the body generally , however, bu t becomesomewhat local ized in specia lglands l ike the l iver

,the

spleen , etc . Even here theydo not appear to find a veryfavou rable condition

,for they

do not grow extensively inthese places. They are l i kelyto be found in the spleen insmal l groups or centres

,bu t

stained, Sho wing the n o t general ly distributedcharacteristic fo rmin

cultures ; b , Stainedthrough It . Wherever they

to sho w the flagella .

grow they pro duce pO iso n ’

which has been called typ/zotox ine

,and i t i s this poi son chiefly which g1ves

ri se to the fever.Q u i te a considerable n umber of the patho

genic germs are,l ike the typhoid baci l l u s

,more

or less confined to special places . Instead o fdistributing themselves th rough the body afterthey find entrance

,they are restricted to special

organ s. The most common example o f a parasite o f this sort is the tuberculo sis bacillus, thecause of consumption

,scro fu la

,white swel l ing

,

l upu s,etc . (Fig . Although this baci l l u s i s

very common and is able to attack almost anyorgan in the body, i t i s u sual ly very restr icted i n

PARASIT IC BAC T ERIA .

growth . I t may become local i zed in a smal lgland

,a single jo in t

,a smal l spot in the lungs

,or

in the glands of the mesentery,the other parts

of the body remain ing free from infect ion . Notinfrequent ly the whole trouble i s thus confined

FIG . 3 I .—Tuberculo sis bacillus : a, As seen in lung tissue b

,

Mo re magnified c, As sometimes seen in sputum o f co n

sumptive patien ts.

to such a smal l locali ty that nothing serious results. But in other i n stances the baci l l i may aftera time slowly or rapid ly distribute themselvesfrom these centres, attacking more and more ofthe body unti l perhaps fatal resu l ts fo l low in theend . This disease is therefo re common ly of veryslow progress .

Again,we have stil l other parasites which are

n o t thus confined , bu t which , as soon as theyenter the body

,produce a general in fection

,at

tacking the b lood and perhaps near ly al l ti ssuessimu ltaneously . The most typica l example ofth i s so rt i s an t/zrax or malignan t pustulc, a diseasefortunately rare i n man (Fig . Here thebaci l l i mu l tip ly in the blood, and very soon ageneral and fatal in fection of the who l e bodyarises

,resu lting from the abundance of the ba


ci l l i everywhere . Some of the Obscu re di seasesknown as blo o a’ po iso ning appear to be of the same

general n atu re,

these diseases t e

sult ing from a verygeneral invasion ofthe whole body bycertain pathogen icbacteria .

In general, then ,we see that the so

cal led germ diseases resu l t from the

FIG . 3 2 .—An tbrax bacillus (splenic

actIO n upon thefever) . body of po ISo n s

produced by bacterial growth . Differences in the natu re of thesepoisons produce di fferences in the character ofthe disease, and diff erences in the parasit ic powers o f the differen t species of bacteria producewide di fferences in the cou rse of the diseases andthei r relation to external phenomena .

WHAT D ISEASES ARE DUE T o BAC T ERIA ?

I t i s,of cou rse

,an ext remely importan t matter

to determine to what exten t human diseases arecaused by bacteria . It i s n o t easy

,nor indeed

possible,to do this to - day with accu racy . I t i s

no easy matter to prove that any particu lar disease is caused by bacteria . To do this i t i s n ecessary to find some particu lar bacteri um presen t inal l cases o f the disease ; to find some method ofgetting i t to grow outside the body in cu ltu remedia ; to demonstrate its absence in heal thy an imals

,or healthy human individual s i f i t be a hu


teriam as i ts cause . Recent study has shown,

however,that thi s is not who l ly true . I t i s tru e

that some diseases do have such a defin ite relat ion to defin i te bacteria . The anthrax germ

,for

example,wi l l a lways produce anthrax

,no matte r

where or how it i s i nocu lated in to the body . So,

a lso,i n qui te a number of other cases distinct

specific bacteri a are associated with di stin ct diseases . But

,on the o ther hand

,there are some

pathogen ic bacteria which are not so defini te intheir action

,and produce di fferen t resu l ts in ao

co rdance with ci rcumstances, the effect varyingboth with the organ attacked and wi th the condition o f the indi vidual . For instance, a considerab le number of differen t types of blood poi soni ng

,septiccemia, pywmia, gangrene, inflammatio n of

w o unds,or fo rmatio n of pus from slight skin

wounds—i ndeed,a host of mi scel laneous trou

bles,ranging al l the way from a sl ight pus forma

tion to a violent and severe blood poison ing—al lappear to be caused by bacteria, and i t i s impo ssible to make out any defini te species associatedw i th the differen t types of these troubles. Thereare three common fo rms of so - cal led pus cocci

,

and these are fo und almost i ndiscriminately wi thvariou s types of inflammatory troubles. Moreo ver

,these species o f bacteria are fo und wi th al

most absolute constancy in and around the body,

even in heal th . They are on the clo thing,on the

sk in,i n the mou th and al imentary canal . Here

they ex ist,commonly doing no harm . They have,

however,the power of doing inj ury if by chance

they get in to wo unds. But thei r power of doingin j ury varies both with the condi tion of the individual and with variation s i n the bacteri a themse lves . If the indi vidual is in a good condition


o f health these bacteria have l i ttl e power o f inj u ring him even when they do get into suchwounds

,whi le at times of feeble vi tal i ty they

may do much more inj u ry,and take the occasion

of any l i tt le o ut or bru ise to enter under the skinand give rise to inflammation and pu s . Somepeople wi l l deve lop sl ight abscesses o r slight inflammatio n s whenever the skin i s bru ised, whi lewi th others such bru ises or cu ts heal at oncewithout trouble . Both are doubtless subj ect tothe same chance of in fection

,bu t the one resists

,

whi le the o ther does not . I n commo n parlance,

we say that such a tendency to abscesses indicates a bad condition of the blood—a phrasewhich means nothing . Further

,we find that the

same species o f bacterium may have varyingpowers of producing disease at di fferen t t imes .Some species are universal in habitants o f theal imentary canal and are ordinari ly harmless

,

while under other condit ion s of u nknown character they invade the ti ssues and give rise to aserio us and perhaps fatal disease . We may thu srecogn ise some bacteria which may be comparedto foreign in vaders

,whi le others are domestic

enemies . The former,l ike the typhoid baci l l u s

,

always produce t rouble when they succeed inentering the body and finding a footho ld . Thelatter

,l i ke the normal in testi nal baci l l i

,are al

ways present but commonly harmless,only under

special condi tion s becoming troublesome . All

thi s shows that there are other factors in determin i ng the cou rse of a disease

,or even the ex ist

ence of a di sease,than the simple presence of a

pecu l iar species o f pathogenic bacteri um .

From the facts j u st stated i t WIll be eviden tthat any l i st of germ diseases wi l l be rather un


certain . Sti l l,the studi es of the last twenty years

o r more have disclosed some defin ite re lations ofbacteria and disease

,and a l ist o f the di seases

more or less defini tely associated with distinctspecies o f bacteria is of in terest . Such a l ist

,

i nc luding on ly wel l - known diseases,i s as fo l lows

Name o f disease . Name o f bacteriumpro ducing the disease .

An thrax (Malignan t pustule) . Bacillus an t/tracis.

C ho lera. Spirillumcho lera asiatica’.

C ro upo us pn eumo n ia. M icro co ccuspn eumo n ia cro upo sa'.

Diphtheria. Bacillus dip/zllzcria'.

G landers. Bacillus mallei.G o n o rrhoea. M icrococcus go n o rrh ea .

Influenza. Bacillus of influen za.

L epro sy . Baci llus leprce .

Relapsing fever. SpirillumObermeieri.T e tanus (lo ckjaw). Bacillus tetan i.T uberculo sis (including co n

sumptio n , scro fula, e tc. ) Bacillus tuberculo sis.

T ypho id fever. Bacillus typlzi abdominalis.

Variou s wound in fections,in cluding septiccemia,

py a rnia , acute abscesses, ulcers, ery sipelas, etc . ,are pro

duced by a few forms of micrococci , resembl ingeach other i n many points bu t di fferi ng sl ightly .

They are found almost indiscriminately in any ofthese wound infections

,and none of them appears

to have any defin ite relation to any special fo rmof disease un less i t be the micrococcus of ery sipelas . The common pus micrococci are groupedu nder th ree Species

,S taplzy lo coccus py ogenes aureus,

S taphy loco ccus py ogenes, and S trey to coccus py ogenes.

These three are the most common,but o thers are

occasional ly found .

I n addition to these,which may be regarded as

demonstrated,the fol lowing diseases are with

more or less certain ty regarded as caused by disti nct specific bacteria : Bronchiti s, endocardi ti s,


di sease after having been cu l tivated for a sho rttime in ord inary cu l tu re media in the laboratory .

This i s easi ly understood upon the suggestionthat i t i s a parasitic baci l l u s and does not thriveexcept u nder parasit i c conditio n s . I ts pathogenic powers can sometimes be resto red by passing i t again through some susceptible animal .One of the most vio lent pathogen ic bacteria isthat which produces antbrax

,bu t thi s loses i ts

pathogenic powers i f i t i s cu l ti vated fo r a co n

siderable period at a high temperature . Themicrococcu s which causes fowl c/zo lera lo ses i tspower if i t be cu l ti vated in common cu lture media

,

care being taken to al low several days to elapsebetween the successive inocu lation s in to n ew

cu l ture flasks . Most pathogenic bacteria canin some way be so treated as to su ff er a dimin utio n or complete loss of thei r powers of producing a fatal disease . On the other hand

,other

condi tions wi l l cause an increase in the v i ru lenceof a pathogen ic germ . The v iru s which produceshydrophobia is increased i n vio lence if i t i sinocu lated into a rabbit and subsequ ently takenfrom the rabbit for further i nocu lation . T he

fowl cholera micrococcus,which has been weak

ened as j u st mentioned,may be restored to i ts

original v io lence by inoculating i t in to a smal lbird

,l ike a sparrow

,and inocu lat ing a second

bi rd from th is . A few such inocu lations wi l lmake i t as act ive as ever . These variation sdoubt less ex ist among the species i n Nature aswel l as in artificial cu l tures . The bacteriawhich produce the v ariou s wound infectio ns andabsce sses

,etc .

,appear to vary under normal con

dit io n s from a type capable o f producing vio len tand fatal blood poi soning to a type producing


only a simple abscess,or even to a type that i s

enti rely innocuous. I t i s thi s factor,doubt less,

which in a large measure determines the severi tyof any epidemic of a bacterial con tagiou s disease .

SUSC EPT IBI L IT Y O F T HE IND IV IDUAL .

The very great modification of our ear lyv iews has affected o u r ideas as to the powerwhich indiv iduals have of resisting the invasionof pathogen ic bacteria . I t has from the fi rstbeen understood that some ind iv iduals are moresusceptib le to disease than others

,and in attempt

ing to determine the sign ificance of this factmany valuable and interesting discoveries havebeen made . After the exposu re to the diseasethere fo l lows a period of some l ength in whichthere are no discernible effects . Thi s i s fo l lowedby the onset o f the disease and its developmentto a cri si s

,and

,i f this be passed , by a recovery .

The general course o f a germ disease i s dividedin to three stages : the stage of incubatio n

,the

development of the disease,and the reco very . The

susceptibi l i ty o f the body to a disease may bebest considered under the three heads of Invasion

,Resistance

,Recovery .

M eans of I nvasio n —In o rder that a germ disease shou ld arise in an individual

,i t i s fi rs t n e

cessary that the special bacterium which causesthe disease shou ld get i nto the body . Thereare several channel s th rough which bacteria canthus find entrance ; these are through themouth

,through the nose

,through the sk in

,and

occasional ly th rough excreto ry ducts . Thosewhich come th rough the mouth come with the


food or drink which we swal low ; those whichenter through the nose mu st be traced to the ai r ;and those which enter through the ski n come inmost cases through con tact wi th some in fectedobj ect

,such as direct contact wi th the body of

an infected person or his cloth ing or some obj ectshe has handled

,etc . Occasional ly

,perhaps

,the

bacteria may get into the sk in from the air,but

thi s is certain ly un common and confined to a fewdiseases . There are here two facts of the utmostimportance fo r every o n e to understand : fi rst

,

that the chance o f disease bacteria being carriedto us through the ai r is very sl ight and confin edto a few diseases

,such as smal lpox

,tubercu lo

sis,scarlet fever ; etc . , and, second ly, that the un

in j u red skin and the uninj ured mucous membranealso i s almost a sure protection against the ihvasio n of the bacteria . If the sk in i s who le

,

withou t bru i ses o r cuts,bacteria can seldom

,i f

ever,find passage through it . These two facts

are o f the u tmost importance, since of al l sou rcesof in fection we have the least power to guardagain st i nfectio n through the ai r

,and since of al l

mean s o f en trance we can guard the skin wi ththe greatest difficu l ty . We can easi ly renderfood free from pathogen i c bacteria by heating it .The material we drin k can simi lar ly be renderedharmless

,bu t we can not by any known means

avo id breathing ai r,nor i s there any known

method of disin fecti ng the ai r,and i t i s impo s

sible for those who have anything to do withsick persons to avo id ent irely having contactei ther with the patient or with infected clo thingor uten si ls .

From the facts here given i t wi l l be seen thatthe indiv idual ’s susceptibi li ty to disease produced


be enti rely su fficient to seize such a foothold,and

then these by mu ltiplying may soon become indefinitely n umerou s . To protect i tse l f

,therefore

,

the human body must destroy every ind i vidua lbacterium

,or at least render them al l incapa

ble o f growth . Thei r marve l lous reproductivepowers give the bacteria an advantage i n the batt le . O n the other hand

,i t takes t ime even for

these rapid ly mu ltip ly ing beings to become su fficiently n umerous to do i nj u ry . There is thu s aninterval after the ir penetration in to the bodywhen these invaders are weak in numbers . During this interva l— the period of incubat ion— thebody may organ ize a resi stance su fficien t to expel them .

We do not as yet thoroughly understand theforces which the human organism is able to arrayagainst these i nvading foes. Some of its methods o f defence are

,however

,al ready in tel l igible

to u s,and we know enough

,at al l events, to give

u s an idea of the intensi ty of the confl ict that i sgoing on

,and of the vigo rous and powerfu l forces

which the human organ ism is able to bring againsti ts invading enemies .In the fi rst place

,we notice that a majo ri ty of

bacteria are utterly unable to grow in the humanbody even if they do find entrance . There areknown to bacterio logists to - day many hundreds

,

even thousands of species,bu t the vast majori ty

o f these find in the human tissues condition s sohosti le to thei r l i fe that they are u tter ly un able togrow therein . Human flesh or human blood wil lfu rn ish excel len t food for them if the individu albe dead

,but l iving human flesh and blood in some

way exerts a repressing influence upon them whichis fatal to the growth of a vast majority of spe


cies . Some few species,however

,are n o t thu s

destroyed by the hosti l e agencies of the ti ssuesof the animal

,but are capable o f growing and

multiplying in the l iving body. These alone arewhat consti tute the pathogenic bacteria, since, o fcou rse

,these are the on ly bacte ria which can pro

duce disease by growing in the ti ssues o f an an i

mal . The fact that the vast majori ty of bacteriacan no t grow in the l iving organ i sm shows clearlyen o ugh that there are some co ndi tions existing in

the l iv ing tissue hosti le to bacterial l i fe . Therecan be l i tt le doubt

,moreover

,that i t i s these same

hosti l e condi tions,which enable the body to resist

the attack of the pathogenic species i n caseswhere resistance i s successfu l ly made.

What are the forces arrayed against these invaders ? The essentia l n a ture of the batt le appears to be a production of poi sons and counterpoi so ns. I t appears to be an u ndo ub ted fact thatthe fi rst step in repe l l ing these bacteria i s to floodthem with certain poisons which check thei rgrowth . In the blood and lymph of man and

other animal s there are present certain productswhich hav e a di rect deleterio us influence upon thegrowth of micro - o rgan i sms . The existence ofthese poiso ns is undoubted

,many an experiment

having directly attested to thei r presence in theblood o f animal s. Of their natu re we know veryli tt le

,but of their repressing influence upon bac

terial growth we are sure . They have been namedalex ines

,and they are pro duced in the l i ving tis

su e,al tho ugh as to the method of their pro

ductio n we are in ignorance. By the aid ofthese poiso ns the body is able t o prevent thegrowth of the vast majori ty of bacteria which

ge t i n to its t issues . Ordinary micro - organi sms


are k i l led at on ce,for these alex ines act as anti

septics,and common bacteria can no more grow

in the l iving body than they cou ld in a sol u tioncontain ing other poisons . Thus the body has aperfect protection again st the majo ri ty of bacteria. The great host of species which are foundin water

,mi lk

,ai r

,i n our mouths or cl inging to

our sk in,and which are almost omnipresen t i n

Nature, are capable of growing wel l enough in o r

dinary l i fe less organ ic foods ; bu t j ust as soon asthey succeed in finding entrance into l iv ing humanti ssue thei r growth i s checked at on ce by theseanti septic agents which are poured upon them.

Such bacteria are therefo re not pathogenic germs,

and not sources of trouble to human heal th .

There are,on the o ther hand

,a few species of

bacteria which may be able to retain thei r lo dgmen t i n the body in spi te of th is attempt of theindi vidual to get rid of them . These

,of course

,

constitu te the pathogen ic species,or so - cal led

disease germs . Only such species as can overcome this fi rst resi stance can be disease germs

,

for they alone can retai n thei r foothold in thebody .

But ho w do these species overcome the poisons which k il l the othe r harmless bacteria ?They

,as wel l as the harmless forms, find these

alex ines in j urious to thei r growth,bu t in some

way they are able to counteract the poisons . I nthi s general discu ssion of poisons we are deal ingwith a subj ect which i s somewhat obscure

,but

apparen tly the pathogenic bacteria are able toovercome the alex i nes of the body by producingin their tu rn certain o ther products which neutraliz e the alexines, thu s annu l l ing their action .

These pathogen ic bacteria,when they get in to


FIG . 3 3 .—White blo od co rpuscles and o ther phago cy tes a,

tio n ary fo rm; b , Mo tile fo rm; c, Phago cy te with a bacteriumhalf engulfed ; d, Phago cy tes co n tain ing bacteria either deado r alive e

,Phago cy te lo aded with bacteria.


tion,and the corpuscles leave the b lood - vessel s

and sometimes form a sol id phalanx completelysu rrounding the invading germs. Their co llec

tion at these poin ts may make i tse l f seen external ly by the phenomenon we cal l inflammatio n .

There is no question that the corpuscles en ~

gage in confl i ct with the bacter ia when they thussu rround them . There has been n o t a l i tt le dispute

,however

,as to the method by which they

carry on the confl ict. I t has been held by somethat the corpuscl es actual ly take the bacteria in totheir bodies

,swal low them

,as i t were

,and subse

quently digest them (Fig. 3 3 c, a’

,c) . This idea

gave rise to the theory of p/tagocy to sis, and thecorpuscles were consequently named phago cy tes.

The study of several years has,however

,made i t

probable that thi s is not the ordinary method bywhich the corpuscles destroy the bacteria . Ao

cording to our present knowledge the method i sa chemical one . These cel ls

,when they thus co l

lect in quanti t ies around the in vaders,appear to

secrete from thei r own bodies certain in j u riou sproducts which act upon the bacteria much as dothe alex ines already mentioned . These new bodies have a decided ly in j u rious e ffect upon themultip lying bacteria ; they rapid ly check thei rgrowth

,and

,acting i n un ion with the alex ines

,

may perhaps enti re ly destroy them .

After the bacteria are thu s k i l led,the white

blood - corpu scl es may load themselves with thei rdead bodies and carry them away (Fig . 3 3 d, e) .Sometimes they pass back in to the blood streamand carry the bacteria to variou s parts o f thebody fo r el imination . Not infrequently the whitecorpu scles die i n the contest

,and then may ao

cumu late in the fo rm ofpus and make their way

1 54 T HE ST ORY O F GERM L IFE.

through the sk in to be discharged direct ly . T he

batt le between these phagocytes and the bacteriagoes on vigorously . If i n the end the phagocytesprove too strong fo r the in vaders

,

'

the bacteriaare gradual ly al l destroyed, and the attack is t e

pelled. Under these ci rcumstances the individualcommonly knows nothing of the matter. Thisconfl i ct has taken place entirely without any conscio usn ess o n his part, and he may not even knowthat he has been exposed to the attack of thebacteria : In other cases the bacteria prove toostrong for the phagocytes . They mu ltiply toorapidly, and sometimes they produce secretion swhich actual ly drive the phagocytes away . Commo n ly , as al ready noticed

,the co rpuscles are at

tracted to the point of invasion,but in some cases

,

when a particu larly deadly and vigorou s speciesof bacteria i nvades the body

,the secret ions pro

duced by them are so powerfu l as actual ly todr1ve the corpuscles away . Under these ci rcumstances the invading hosts have a chance to mult iply un impeded , to d istribute themselves over thebody

,and the di sease rapid ly fo l lows as the resu l t

of thei r po i soning action on the body ti ssues .It i s plain

,then

,that the human body is n o t

helpless in the presence of the bacteria o f disease,

but that i t i s suppl ied with powerfu l resistan tforces. I t mu st not be supposed

,however

,that

the outl ine of the action of these fo rces j u st givenis anything l ike a complete account of thematter ;n o r must i t be i nferred that the resistance is in allrespects exactly as outl in ed . The subject has on lyrecently been an object of i nvestigation

,and we are

as yet in the dark in regard to many of the facts .

The fu tu re may requ ire us to modi fy to some exten t even the br ief o ut l ine which has been given .

T HE ST ORY OF G ERM L IFE.

REC O VERY FROM G ERM DISEASES.

These resi sting forces are not always su fficientto drive o ff the invaders. The o rgan isms mayretain thei r ho ld in the body for a time andeventual ly break down the resistance . After thi sthey may mu ltip ly unimpeded and take en tirepossession of the body . As they become moren umerous thei r poi sonous products increase andbegin to produce di rect poi soning effects on thebody . The incubation period is over and the disease comes o n . The disease now run s i ts cou rse.

I t becomes common ly more and more severe unti la cri si s i s reached . Then

,un less the poisoning is

so severe that death occurs,the eff ects pass away

and recovery takes place.

Bu t why shou ld not a germ disease be alwaysfatal ? I f the bacte ria thu s take possession of thebody and can grow there

,why do they not a lways

conti nue to mu ltiply u n ti l they produce sufficientpoison to destroy the l i fe o f the individualSuch fatal resu l ts do

,of cou rse

,occu r

,but in by

far the larger proportion of cases recovery final lytakes place.

Plain ly,the body must have another set of

resi sting forces which i s concerned i n the finalrecovery. Although weakened by the po isoningand suffering from the disease, i t does n o t yieldthe battle

,but somewhat slowly organizes a new

attack upon the invaders. For a time the mu ltip lying bacteri a have an unimpeded course andgrow rapidly ; bu t final ly thei r fu rther i ncrease i schecked

,their v igour impaired

,and after thi s they

dimin i sh in numbers and are final ly expel led fromthe body entirely . Of the natu re of thi s new re

sistance bu t l i tt le i s yet known . We notice,in


the fi rst p lace,that common ly after su ch a reco v

ery the individual has decidedly increased resistance to the disease . This increased resistancemay be very lasting

,and may be so considerable

as to give almost complete immunity from thedisease fo r many years

,o r for l i fe . O ne attack

of scarlet fever gives the i ndividual great immun ity for the futu re . On the o ther hand

,the re

sistance thu s derived may be very temporary , asi n the case of diphtheria . But a certain amoun to f resi stance appears to be always acqu i red.

This power of resisting the activi t ies of the parasi tes seems to be increased during the progressof the disease

,and

,i f i t becomes su fficien t , i t

final ly drives O ff the bacteri a befo re they haveproduced death . After th i s

,recovery takes place .

To what this newly acqui red resisting power i sdue i s by no means clear to bacterio logists, although certain factors are already known . I tappears beyond question that i n the case of certain diseases the cel l s of the body after a timeproduce substances which serve as antidotes tothe poisons produced by the bacteria during thei rgrowth in the body—antito x ines. In the case ofdiphtheria

,for in stance

,the germs growing in the

throat produce po isons which are absorbed by thebody and give r ise to the symptoms of the di sease ; bu t after a time the body cel l s react, andthemse lves produce a cou nter tox ic body whichneutral i z es the poisonou s effect of the diphtheri apoison . This substance has been isolated fromthe blood of an imals that have recovered from anattack o f diphtheria

,and has been cal led diphthe

ria antito x ine. But even with thi s know ledge therecovery is n o t fu l ly explained . This antitox ineneutral i zes the effects of the diphtheria tox ine,


and then the body develops strength to dri ve o ffthe bacteria which have obtai ned lodgment i n thethroat . How they accomplish thi s latter achievement we do not know as yet . The anti toxinedeveloped simply neutral izes the effects o f thetox ine . Some other force must be at work to getrid of the bacteria

,a force which can only exert

i tsel f after the poisoning effect o f the poison i sneutral i zed . In these cases

,then

,the recovery i s

due,fi rst

,to the development in the body of the

natural antidotes to the tox ic po isons , and , second ,to some other unknown force which drives o ff theparasites .These facts are certain ly su rprising. I f one

had been asked to suggest the least l ike ly theoryto explain recovery from disease

,he cou ld hard ly

have fo und one more un l ikely than that the bodycel l s developed during the disease an an tido te tothe poison which the disease bacteria were producing. Nevertheless

,i t i s beyond question that

such antidotes are formed during the cou rse ofthe germ diseases . I t has not yet been shown inal l di seases

,and i t wou ld be en ti rely too much to

claim that th is is the method of recovery i n al lcases . We may say

,however

,i n regard to bacte

r ial di seases in general , that after the bacteria enter the body at some weak poin t they have fi rst abattle to fight with the resisting powers of the body,which appear to be part ly biological and partlychemical . These resi st ing powers are in manycases enti re ly su fficient to p reven t the bacteriafrom obtaining a foothold . If the invading hostovercome the resi sting powers

,then they begin

to mu ltiply rapid ly, and take possession of thebody o r some part o f i t . They conti nu e t o growuntil ei ther the individual dies or something o c


i n method of attack,and in the part o f the body

which they seiz e upon as a n ucleus fo r growth .

They differ in violence and i n the character of thepoi sons they produce

,as wel l as in thei r power of

overcoming the resisting powers o f the body .

They di ffer at different times i n thei r powers ofproducing disease . In sho rt

,they Show such a

large number of diff erent methods of action thatn o general statements can be made which wi l l apply universal ly

,and n o one method of guarding

against them or in d ri ving them o ff can be hopedto apply to any extended l ist of diseases .

DISEASES C AUSED BY O T HER O RG ANISMS T HAN

BAC T ERIA .

Although the purpose of thi s work i s to dealprimari ly with the bacterial world

,i t wou ld hard ly

be fi tting to leave the subj ect without some reference to di seases caused by organisms which donot belong to the group of bacteria . While mostof the so cal led germ diseases are caused by thebacteria which we have been studying in theprevious chapters

,there are some whose incit ing

cause i s to be found among organisms belongingto other groups . Some of these are plants of ahigher o rgan ization than bacteria

,but o thers are

undoubtedly microscopi c animals . Their l i fehabits are somewhat di fferen t from those o fbacteria

,and hence the cou rse o f the di seases is

common ly di ff erent . Of the di seases thus produced by microscopic animals or by higher plan ts

,

one or two are of impor tance enough to deservespecial ment ion here .

M alaria—The most important of these diseases i s malaria in i ts various forms

,and known


under various names—Mills and fever,autumnal

fever, etc. This disease,so common almost

everywhere,has been studied by physicians and

scien tists for a long time, and many have beenthe causes assigned to i t . At one time i t wasthought to be the resu l t o f the growth of a hao terium

,and a distinct bacillu s was described as pro

ducing i t . I t has final ly been shown , however,to be caused by a microscopic organism belonging to the group of unicel l u lar an imals, and some

Flo . 3 4.—Malarial o rgan ism : Figs. a to g sho w the gro wth o f

the parasite w ithin the blo o d co rpuscle ; o is the o rgan ism in

all cases ; 5 , the spo res . Fig. I is the so -called cresen tic bo dywhich develo ps thro ugh Fig. 2 , in to the flagellate fo rm, sho wn

at 3 . T he sign ificance o f 1 , 2 , and 3 are n o t kn o wn .

what closely related to the wel l - known amo eba .

Thi s o rgan ism is shown in Fig. 3 4. The who leh istory of the malaria l organ i smi s not yet known .

The fol lowing statements comprise the most importan t facts known in regard to it

,and i ts rela

tio n to the disease i n man .

Undoubtedly the malarial germ has somehome outside the human body

,but i t i s not y et

very definitely known what th is external home i s ;n o r do we know from what sou rce the human para


si te is derived. I t appears probable that waterserves in some cases as i ts mean s o f tran sferenceto man

,and ai r in other cases . From some ex

ternal source i t gains access to man and findsit s way in to the blood . Here i t attacks thered b lood corpuscles, each malaria l organismmaking its way i nto a single one (Fig. 3 4 a) .Here it now grows, i n creasing in si ze at theexpense of the substance of the corpu scle

(Fig. 3 4 a—f ) . As i t becomes larger i t becomesgranu lar

,and soon shows a tendency to separate

into a n umber of i rregu lar masses (Fig. 3 4 f ) .Final ly i t breaks u p into many minute bodiescal led spores (Fig. 3 4g) . These bodies break outo f the corpuscle and for a time l i ve a free l i fe inthe b lood (Fig. 3 4 lz) . After a time they makethei r way into o ther red blood corpuscles, developi n to new malarial amo eboid parasites

,and repeat

the growth and sporu lation . This process can ap

paren tly be repeated many times without check .

These organisms are thus to be regarded as

parasites o f the red corpuscl es . I t i s,o f cou rse

,

easy to bel ieve that an exten sive parasiti sm and

destruction of the co rpuscles wou ld be disastrousto the health of the individual, and the severityof the disease wi l l depend upon the exten t o f theparasiti sm . Corresponding to th is l i fe h istory o fthe organism

,the disease malar ia i s common l y

characteri zed by a decided intermittency,period s

of chi l l and fever alternating wi th periods of intermissio n i n which these symptoms are abated .

The paroxysms of the disease , characteri zed bythe chi l l

,occu r at the time that the spores are

escaping from the blood - corpuscles and floatin gin the blood . After they have agai n found thei rway in to a blood - corpu scle the fever dimin i shes

,


ficial method yet devised . Its whole h istory i stherefore n o t known . I t doubtless has somehome outside the b lood of animals

,and very

l ikely i t may pass through other stages of a metamorphosis in the bodies of other an imals . Mostparasi tic an imals have two or mo re ho sts uponwhich they l i ve, alternating from one to the other,and that such is the case with the malaria l parasi te i s at l east probable . But as yet bacterio logists have been unable to discover anything verydefinite i n regard to the matter. Unti l we canlearn something in regard to its l i fe ou tside theblood of man we can do l i tt le in the way of devising methods to avoid i t .Malaria di ffers from most germ diseases in the

fact that the organ isms which produce i t are n o teliminated from the body in any way . In mostgerm diseases the germs are discharged from thepatien t by secretions or excretions o f some kind

,

and from these excretions may readi ly find thei rway into other indiv idual s. The malaria l organi sm is not di scharged from the body in any way,and hence is no t con tagiou s . If the parasite do espass part of i ts h i sto ry in some o ther animalthan man

,there must be some means by which it

passes from man to i ts o ther host . I t has beensuggested that some of the insects which feedupon human blood may serve as the second hostand become inocu lated when feeding upon suchblood . This has not yet been demonstrated , ho wever. At al l events

,the malarial o rgan ism is

no t no rmal ly discharged from man and the di sease i s not contagiou s.Several other microscopic an imals occur as

parasites upon man,and some of them are so

defini tely associated with certain diseases as to

C OMBAT ING PARASIT IC BAC T ERIA. 1 65

lead to the belief that they are the cause of thesedi seases. The on ly one o f very common occu rrence i s a species known as Amoeba co li, which i sfound in cases of dysentery . In a certain typeof dysen tery this organ ism i s so un i versal ly fo undthat there is l i tt le doubt that i t i s i n some veryin timate way associated with the cause o f the di sease . Defin ite proof o f the matte r i s

,however

,

as yet wanting .

On the side of p lan ts,we find that several

plants of a higher organizat ion than bacteria maybecome parasi tic u pon the body of man and produce various types of disease These plan ts belong most ly to the same group as the mou lds

,

and they are especial ly apt to attack the skin .

They grow in the skin,particu larly under the hai r

,

and may send thei r thread li ke branches into someof the subdermal tissues. Thi s produces i rri tat ion and inflammation of the sk in

,resu l ting i n

troub le,and making sores difficu l t to heal . So

long as the plant con tinues to grow,the so res

,of

course,can not be healed

,and when the o rgan

i sms get in to the sk in under the h ai r i t i s frequently di fficu l t to destroy them . Among thediseases thus cau sed are ringwo rm,

t/zrus/z,alopecia

,

etc .

CHAPTER VI .

MET HODS O F C OMBAT ING PARASIT IC BAC T ERIA .

T HE chief advan tage of knowing the cau se ofdisease i s that i t gives u s a van tage ground fromwhich we may hope to find mean s of avoiding it sevi l s . The study of medicine in the past history

T HE ST ORY OF GERM L IFE.

of the world has been almost pu rely empi rical ,with a very l i tt l e of scientific basis . G reat hopesare n o w enter tained that these new factswi l l pl acethi s matter u pon a more stri ct ly scien ti fic foundation . Certain ly in the past twenty - five years

,

since bacterio logy has been studied,more has

been done to solve problems connected with disease than ever before . Thi s new knowledge hasbeen particu larly di rected toward means of avoiding disease . Bacterio logy has thu s far bornefrui t large ly in the l in e of preven ti ve medicine

,

al tho ugh to a certain extent al so along the lineof curati ve medicme . This chapter wi l l be devoted to con sidering how the study of bacterio logy has con tributed direct ly and indi rect ly too ur power of combating di sease .

PREVENT IVE MEDIC INE.

In the study o f medicine in the past centu riesthe on ly aim has been to discover methods ofcuring disease ; at the presen t time a large andincreasing amoun t o f study i s devoted to themethods o f prevent ing disease . Preventive medicine is a development of the last few y ears, andi s based almost who l ly upon ou r knowledge ofbacter ia . This subj ect is yearly becoming o fmore importance . Forewarned i s fo rearmed

,and

i t has been found that to know the cause of adisease i s a long step toward avoiding it . Assome of our contagious and epidemic diseaseshave been studied i n the l ight of bacterio logicalk now l edge

,i t has been found possible to deter

mine not on ly thei r cau se,bu t also how in fection

i s brought about,and con sequent ly how conta

gion may be avoided . Some of the resu lts which


spread of disease . Its value i s seen in the fact thatthere has been a constant decrease in the deathrate since modern ideas of san itation began tohave any influence

,and in the fact that ou r

general epidemics are less severe than i n fo rmeryears

,as wel l as in the fact that mo re people

escape the di seases which were in fo rmer timesalmost un iversal .The study of preventi ve medicine takes in to

v iew several facto rs,al l connected w i th the

method and mean s of contagion . They are thefo l lowing :

T be S o urce of I nfectio usM atcrial.—It has beenlearned that fo r most diseases the infectio u s material comes from indiv iduals su ffering with thed isease

,and that except i n a few cases, l ike ma

laria,we must always look to individuals su ffering

from disease fo r all sources o f con tagion . I t i sfoun d that pathogen ic bacteria are in al l thesecases e l imi nated from the patien t i n some way

,

ei ther from the alimen tary canal or from skin secre tio ns o r otherwise, and that any nu rse withcommon sense can have no difficu l ty i n determin ing in what way the infectious material i sel iminated from her patients . When thi s fact i sknown and taken into consideration i t i s a com

paratively easy matter to devise val uable precaution s against distribu tion of such material . I t i sthus of n o small importance to remember that thesimple presence of bacteria i n food or drink is o fno significance un less these bacteria have comefrom some sou rce o f disease in fection .

T lzeM etlzo a’

of D istributio n—The bacteria mustnext get from the original sou rce of the disease tothe new susceptible individual . Bacteria have noindependen t powers of dist ribution un less t hey

C OMBAT ING PARASIT IC BAC T ERIA. 1 69

be immersed in l iqu ids,and therefore thei r pas

sage from individual to individual must be a passive one . They are readi ly transferred

,however

,

by a number of different means,and the study of

these means is aiding much in checking con tagionStudy along thi s l ine has shown that the meansby which bacteria are carried are Several . Firstwe may no tice food as a distributo r . Food maybecome contaminated by infectio us material i nmany ways ; for example, by contact with sewage,o r wi th pol luted water

,o r e ven wi th eating u ten

sils which have been used by patien ts . Water i sal so l ike ly to be contam inated with in fectiou smaterial

,and is a ferti le source for distributing

typhoid and cholera . Milk may become contaminated i n a variety of ways

,and be a sou rce of dis

tributing the bacteria which produce typhoidfever

,tubercu losi s

,diphtheria

,scar le t fever

,and

a few o ther less common di seases . Again , ifected clothing,

bedding,o r eating utensi l s may

be taken from a patient and be used by anotherindividual without proper cleansing . Direct contact

,or contact with infected animals

,fu rn ishes

another method . Insects sometimes carry thebacteria from person to person

,and in some dis

eases (tubercu losi s, and perhaps scarlet fever andsmal lpox ) we must look to the ai r as a distributo r o f the in fectio u s materi al . Knowledge ofthese facts i s helping to accoun t fo r mu lti tudeso f mysterious cases o f infection

,especial ly when

we combine themwith the known sou rces of contagio us matter .M eans of Invasio n—Bacterio logy has shown u s

that di fferent species of parasi tic bacteria havedi fferent means of entering the body

,and that

each must enter the proper place in order to get


a foothold. After we learn that typho id in fect io ns materia l must enter the mouth in o rder top roduce the disease ; that tubercu losi s may findentrance through the nose in breath ing, whi l etypes o f b lood poisoning enter on ly throughwounds or broken skin

,we learn at once funda

mental facts as to the proper methods of meetingthese dangers . We learn that w ith some diseasescare exerci sed to preven t the swal lowing of in fect io ns material i s su fficien t to prevent contagion

,

whi le wi th others th is i s enti rely insu fficien t .When al l these facts are understood i t i s almostalways perfect ly possibl e to avoid contagion ; andas these facts become more and more widely knowndirect cont agion i s su re to become less frequent .Above al l

,i t i s tel l ing u s what becomes of the

pathogenic bacteria after being el iminated fromthe body of the patient ; how they may ex ist fo ra long time sti l l acti ve ; ho w they may l urk i nfil th or water dorman t bu t al ive

,or how they may

even mu ltiply there . Preventivemedicine is tel ling us how to destroy those thus lying in wai t fo ra chance of infection

,by discovering disin fect

an ts and tel l ing us especial ly wlzerc and ref/zen tou se them . I t has a lready taught us how to crushout certain forms of epidemics by the propermeans of destroying bacteria, and i s l esseningthe dangers from contagious diseases . I n sho rt

,

the study of bacteriology has brought us i nto acondition where we are no longer help less in thepresence of a raging epidemic. We no longer si tin helpless dismay

,as did ou r ancestors

,when an

epidemic en ters a commun ity,but

,knowing thei r

causes and sou rces,set abou t at once to remove

them . As a resu lt,severe epidemics are becoming

comparatively sho rt - l ived .


The demonstration that pu trefaction and decay were cau sed by bacteria

,and the ear ly proof

that the si lkworm disease was produced by a

micro - organ ism, led to the suggestion that the ihflammat o ry di seases accompanying wounds weresimi larly caused . There are many strik ing similarities between these troubles and pu trefaction

,

and the suggestion was an obvious one . At fi rst,

however,and fo r qui te a number o f years

,i t was

impossible to demonstrate the theory by findingthe distinct species of micro - organ isms which produced the tro ubles . We have al ready seen thatthere are several differen t species o f bacteria whichare associated with th is general class of diseases

,

bu t that no specific o n e has any particu lar re lationto a defini te type of i nflammation . This fact madediscoveries in this connection a slow matter fromthe microscopical standpoin t . But long beforethi s demonstration was final ly reached the theoryhad received practical appl icat ion in the form ofwhat has developed into antiseptic or asepticsurgery .

Anti septic su rgery i s based simply upon theattempt to preven t the entrance of bacteria in tothe surgical wound . I t i s assumed that i f theseorganisms are kept from the wound the heali ngwi ll take place withou t the secondary fevers andinflammatio ns which occur i f they do get a chanceto grow in the wound . The theo ry met with decided opposit ion at first

,but accumu lating facts

demonstrated its valu e,and to - day i ts methods

have been adopted everywhere i n the civi l i zedwor ld . As the evidence has been accumu lating

,

surgeons have l earned many importan t facts,fore

most among which is a knowledge of the commonsources from which the infection of wounds o c

C OMBAT ING PARASIT IC BAC T ERIA.

curs . At fi rst i t was thought that the ai r was thegreat sou rce o f in fection

,but the ai r bacteria have

been found to be u sual ly harmless . I t has ap

peared that the more common so urces are thesurgeon ’s i n struments

,or his hands

,or the cloth

ing or sponges which are al lowed to come in contact with the wounds . I t has also appeared thatthe bacteria which produce this class of troublesare common species

,existing everywhere and u n i

versally present around the body , cl inging to theclo thing or skin

,and always on hand to enter the

wound if occasion offers . They are always present

,b ut common ly harmless. They are not fo r

eign i nvaders l ike the more v io len t pathogenicspecies

,such as those of Asiati c cho lera , but may

be compared to domestic enemi es at hand . I t i sthese ever- present bacteria which the su rgeonmust guard against . T he methods by which hedoes thi s need not detain us here . They consi stessential ly i n bacterio logical clean l i ness Theoperation is performed wi th steri l i zed instrumentsu nder most exacting condi tions of cleanl iness .

The resu l t has been a complete revo lut ion insu rgery . As the methods have become betteru nderstood and more thoroughly adopted

,the in

stances o f secondary troubles fo l lowing su rgicalwounds have become less and less frequent un ti lthey have practical ly disappeared i n al l simplecases . To - day the su rgeon recognises that wheni nflammatory troubles of th is sort fo l low simplesurgical wounds i t i s a testimony to his care lessness . The ski lful su rgeon has learned that wi ththe precautions which he is able to take to - dayhe has to fear on ly the direct effect o f the shockof the wound and its subsequent di rect i nfluence ;but secondary su rgical fevers

,blood po ison ing

,


and su rgical gangrene need not be taken in to consideration at al l . I ndeed

,the modern su rgeon

hardly knows what su rgical gangrene is,and bac

terio lo gists have had practical ly no chance tostudy i t . Secondary in fections have largely disappeared

,and the su rgeon is concerned simply

wi th the effect of the wound i tse lf,and the power

of the body to withstand the shock and subse

quently heal the wound .

With these secondary troubles n o longer todistu rb him

,the su rgeon has become more and

more bo ld . Operations fo rmerly n o t dreamed ofare now performed witho u t hesitation . I n formeryears an operation whi ch opened the abdomina lcavi ty was not thought possible

,or at least i t was

so nearly certain to resu l t fatal ly that i t was re

sorted to on ly o n the last extremity ; whi le to - daysuch operations are hardly regarded as serio u s .Even brain surgery i s becoming more and morecommon . Possibly our surgeons are passing toofar to the other extreme

,and

,feel ing thei r power of

performing so many operation s without inco n venience or danger

,they are u sing the knife in cases

where i t wou ld be better to leave Nature to hersel f for her own heal ing . But

,be this as i t may ,

i t i s impossible to estimate the amoun t of su ffering prevented and the n umber of l ives saved bythe mastery of the secondary inflammatory troubles which used to fo l low su rgical wounds .

Preventive medicine , then , has for i ts obj ectthe preven tion rather than the cure of di sease .

By showing the cau ses of disease and tel l ing us

where and ho w they are contracted,i t i s tel l ing

u s how they may to a large extent be avoided .

Unl ike practical medicine,th i s subj ect i s one

which has a direct relation to the general publ ic.


n ity i s beyond quest ion . Apparent ly al l in fect ion s diseases from which a rea l recovery takesplace are fo l lowed by a certai n amount of protect io n from a second attack ; bu t wi th some diseases the immuni ty i s very fleeting

,whil e wit h

others it i s more lasting . Diseases which produce a general in fection of the who le system are

,

as a ru le,more l ikely to give ri se to a lasting

immunity than those which affect on ly smal lparts . Tubercu losis

,which

,as al ready noticed

,

i s commonly qu ite local i z ed in the body,has ~lit ~

t l e power o f conveying immunity,whi le a disease

l i ke scar let fever,which affects the whole system

,

conveys a more lasting protection .

Such immunity has long been kn own,and in

the earl ie r years was sometimes voluntari ly ac

qu ired ; even to - day we find some individual smaking use o f the principle . I t appears that ami ld attack of such diseases produces immunityequal ly wel l with a severe attack , and actingupon thi s fact mothers have no t in frequent lyintentionally exposed their chi ldren to certaindiseases at season s when they are mi ld

,i n o r

der to have the disease “over wi th and theirchi ldren protected in the fu tu re . Even the moresevere diseases have at times been thus volun tarily acqui red . I n China i t has sometimesbeen the cu stom thus to acqu i re smal lpox . Suchmethods are decided ly heroic

,and of cou rse to be

hearti ly condemned . But the principle that ami ld type of the disease conveys protection hasbeen made use of in a more logical and defensib leway .

The first in stance of th i s principl e was in vac

cinatio n against smal lpox , now practi sed for morethan a centu ry . Cowpox i s doubt less closely re


lated to smal lpox , and an attack o f the formerconveys a certain amount of protection agai nstthe latter . I t was easy

,therefore

,to i nocu late

man with some of the infectious material fromcowpox

,and thus give him some protection

against the more serious smal lpox . This was apurely empirica l discovery

,and vaccination was

practi sed long before the principle u nder lying i twas understood

,and long before the germ n atu re

of disease was recogn i sed . The principle was rev ived again , however, by Paste u r, and thi s timewith a logica l thought as to i ts value . Whi leworking upon anthrax among animals

,he learned

that here,as in other diseases

,recovery

,when it

occurred,conveyed immun ity. This led him to

ask if i t were no t possible to devise a method ofgiving to an imal s a mi ld form of the di sease andthus pro tect them from the more severe type .

The problemof giving a mi ld type of thi s ex trao rdinarily severe disease was not an easy one . I tcould n o t be done

,of cou rse

,by inocu lating the

an imals with a smal l n umber of the bacteria,for

thei r power of mul tipl icatio n wou ld soon makethem indefinitely numero us . It was necessaryi n some way to dimin i sh thei r violence . Pas

t eur succeeded i n doing this by causing them togrow i n cu l ture flu ids for a time at a high tem

perature . This treatmen t diminished thei r v iol ence so much that they cou ld be inocu lated intocattle

,where they produced only the mildest type

of indisposi tion,from which the animals speedi ly

recovered . But even this mi ld type of the disease was tri umphantly demonstrated to protectthe animals from the most severe form of an

thrax . The di scovery was natural ly hai led as a

most remarkable one,and one which promised

1 78 T HE ST ORY O F GERM L ll-‘

E.

great things in the futu re . I f i t was thus possib le

,by di rect laboratory methods

,to find a

means of inocu lati ng against a seriou s diseasel ike anthrax , why cou ld not the same princip le beapp lied to h uman diseases ? The enthusiasts began at o nce to look forward to a time when al ldi seases shou ld be thu s conquered.

But the principle has no t borne the fru i t atfirst expected . There i s l i tt le doubt that i t mightbe appl ied to quite a number of human diseasesi f a seriou s attempt shou ld be made . Bu t severalobj ections ar ise against i ts wide appl ication . In thefirst place, the inocu lation thus necessary is real lya seriou s matter . Even vaccination

,as i s wel l

known,sometimes, th rough fau l ty methods, re

sults fata l ly, and i t i s a very serious th ing toexperiment upon human beings with anything sopowerfu l fo r i l l as pathogen ic bacteria . The serio usn ess of the disease smal lpox

,its extraordinary

contagiou sness,and the comparatively mi ld resu l ts

of vaccmatio n,have made u s wi l l ing to undergo

vaccination at times of epidemics to avoid thesomewhat great probabi l i ty o f tak ing the di sease .

But mankind is u nwi l l ing to undergo su ch an o pcration , even though mi ld , for the pu rpose ofavoid ing other less severe diseases

,or diseases

which are less l ikely to be taken . We are un

wi l l ing to be inocu lated against mi ld diseases,or against the more severe ones which areuncommon . For in stance

,a method has been

devi sed for rendering an imals immune againstlockj aw

, which wou ld probably app ly equal lywel l to man . But mankind in gen era l wi l l neveradopt i t

,since the danger from lockj aw i s so

smal l . Inoculat ion must then be reserved fordiseases which are so severe and so common

,or

T HE ST ORY OF GERM L IFE.

v en tive i no cu lation has been made,but one based

upon a di fferen t principle . Hydroplzo bia i s certain ly o ne of the most horrible of diseases

,al

though comparati vely rare . I ts rari ty wou ld ef

fectually preven t mankind from submi tting toa general inocu lation against i t

,bu t i ts severi ty

wou ld make one who had been expo sed to i tby the bite of a rabid an imal ready to submi tto almost any treatment that promised to wardo ff the disease . In the attempt to discover amean s o f inocu lating against thi s di sease i t wasnecessary, therefore, to find a method that cou ldbe applied after the time o f exposure—i. e .

,after

the individual had been bitten by the rabid an imal . Fortunately

,the disease has a long per iod

of i ncubation,and one that has proved long

enough fo r the purpose . A method of inocu lat ion against th i s d isease has been devised by Pasteu t

,which can be appl ied after the individua l

has been bi tten by the rabid an imal . Apparently,however

,th i s preven tive inocu lation i s dependent

upon a di fferen t princip le from vaccinatio n or iho culatio n against anthrax . I t does not appear togive rise to a mi ld fo rm of the disease

,th us pro

tecting the individual , but rather to an acqui redto lerance of the chemical poisons produced bythe disease . I t i s a wel l - known physio logical factthat the body can become accustomed to to lerate

poi sons i f in ured to them by successively largerand larger doses . I t i s by this power, apparently,that the inocu lation against hydrophobia producesi ts e ff ect . Material contain ing the hydrophobiapoison (taken from the spinal cord of a rabbi tdead with the disease) i s in j ected into the indiv idual after he has been bitten by a rabid an imal .The poi sonous materia l i n the first in j ection is

C OMBAT ING PARASIT IC BAC T ERIA. 1 8 1

v ery weak , bu t i s fol lowed laterb y a more powerfulinocu lation . The resu l t i s that after a sho rt timethe individual has acqu i red the power of resi stingthe hydrophobia poisons. Before the incubationperiod of the original i nfectious matter from thebite o f the rabid an imal has passed , the inocu latedindividual has so thoroughly acqui red a toleranceof the poi son that he successfu l ly resi sts the attackof the infection . This method of inocu lation thusn eu tral i z es the effects of the disease by an ticipat

i ng them .

The method o f treatmen t of hydrophobia metwith extraordinari ly vio len t opposi tion . For several years i t was regarded as a mistake. But theconstan tly accumu lati ng statist ics from the Pasteur I nsti tu te have been so overwhelmingly onone side as to quiet opposi tion and bring abou t ageneral con vict io n that the method is a success .The method of preven tive inocu lation has n o t

been extensively appl ied to human diseases in ad

di tion to those mentioned . In a few cases a simi larmethod has been used to guard against diphtheria.

Among animals,experiment has shown that su ch

methods can quite easi ly be obtained,and doubt

l ess the same wou ld be true o f mankind if i t wasthought practical o r feasible to apply them. But

,

fo r reasons mentioned,th is feature of preven t ive

medicine wi l l always remain rather unimportant,

and wi l l be confined to a few of the more violen tdiseases.I t may be wel l to rai se the question as to why

a single attack with recovery conveys immun i ty .

This question i s real ly a part o f the one al readydi scu ssed as to the method by which the bodycures disease . We have seen that thi s i s i n partdue to the developmen t of chemical substances

1 8 2 T HE ST ORY O F G ERM L IFE.

which ei ther neut ral ize the poi s'

on s Or act as

.germicide upon the bacteri a,or both

,and perhaps

due in part to an active destruction o f bacteriaby ce l l u lar acti vi ty (phagocytosis) . There is l i tt lereason to doubt that i t i s the same set of activ it ies which renders the an imal immune . The forceswhich drive o ff the invading bacteria in one caseare sti l l p resent to prevent a second

,attack o f the

same species o f bacterium . The length of timedur ing which these fo rces are active and su fficientto Cope with any new invaders determines the

l ength of time duri ng which the immuni ty lasts .U nti l, there fore, we can answer with more exactn ess just . ho w cu re i s brought abou t i n case o fdisease

,we shal l be unable to explain the method

of immun ity .

L IM IT S O F PREVENT IVE MED IC INE .

With al l the advance in preventive medicinew e can not hope to avo id disease entirely . Weare discovering that the sou rces of disease are onal l sides of us

,and so omnipresen t that to avo id

them complete ly i s impossible . I f we were toapply to our l ives al l the safeguards which bacterio lo gy has taught us shou ld be appl ied in orderto avoid the di fferent diseases

,we wou ld su rround

o u rsel ves wi th condi tions which wou ld make l i fei ntolerab le . It wou ld be oppressive enough foru s to eat no food except when i t i s hot

,to drin k

n o water except when boi led,and to drink n o

mi l k except after steri l i zation ; bu t these wou ldn o t satisfy the necessary conditions for avoidingdi sease . To meet al l dangers

,we shou ld handle

nothing which has not been steri l i zed,or shou ld

fol low the handl ing by immediately steri l i z ing the


wise su ccumb earl ier in the struggle is enab led tol ive a few years longer . Whatever be our humanitarian feel ing for the individual

,we can not fai l

to admi t that thi s su rvival o f the weak i s o f nobenefi t to the race so far as the development o fphysical nature is concerned . Indeed

,i f we were

to take into consideratio n simply the physicaln atu re of man we shou ld be obl iged to recommend a system such as the ancient Spartans deve lo ped, of exposing to death al l weakly individnals

,that on ly the strong might live to become

the fathers o f futu re generations. In thi s l ight,

of course,parasitic d iseases wou ld be an assist

ance rather than a detriment to the human race .

Of cou rse such principles wi l l n ever again bedominant amon g men

,and our conscience te l l s u s

to do all we can to help the weak . We shal ldoubtless do al l possible to develop preven ti vemedicine in order to guard the weak against parasi tio organi sms . But i t is at al l events wel l for usto remember that we can never hope to develop thestrength of the human race by shunning evi l

,bu t

rather by combating i t, and the power o f thehuman race to resist the invasions o f these o r

gan isms wi l l n ever be developed by the l ine o faction which guards us from attack . Here, as inother directions

,the prin ciples o f modern human i ty

have,together with their undoubted favou rable

i nfluence upon mankind,certain tendencies toward

weakness. Whi le we shal l sti l l do ou r u tmost todevelop preventi ve medicine in a proper way

,i t

may be wel l for us to remember these facts whenwe come to the practical question of determin ingwhere to draw the l imits of the appl ication ofmethods for preventi ng i n fectious diseases .


C URA T IVE MEDIC INE .

Bacter io logy has h itherto contributed less tocurative than to prevent ive medicine . Nevertheless

,i ts contributions to curative medicine have

not been u n impo r tant,and there is p romise o f

much more in the fu tu re . I t i s,of cou rse

,unsafe

to make predictions fo r the fu ture , bu t the accomplishmen ts of the last few years give much hopeas to further resu lts.

DRUG S .

I t was at first thought that a knowledge o fthe specific bacteria which cause a di sease wou ldgive a ready means of finding specific drugs fo rthe cure of such disease. If a defin ite species o fbacteri um causes a disease and we can cu l ti vatethe o rgan ism in the laborato ry

,i t i s easy to find

some drugs which wi l l be fatal to i ts growth,and

these same drugs,i t wou ld seem

,shou ld be val u ~

able as medicines in these di seases. This hopehas

,however

,proved largely i l lu si ve. I t i s very

easy to find some drug which proves fatal to thespecific germs whi le growing in the cu l tu re mediaof the laboratory

,but common ly these are o f l i tt l e

or no use when applied as medicines. I n the fi rstp lace

,such substances are u sual ly very deadly poi

sons . Corrosive subl imate is a substance whichdestroys al l pathogenic germs with great rapidi ty

,

but i t i s a deadly poison,and can not be used as a

drug in su fficien t quanti ty to destroy the parasi t icbacteria i n the body wi thou t at the same timeproducing poi sonous effects on the body i tse l f.I t i s evident that fo r any drug to be of value inthus destroying bacteria i t must have some spe


cially strong actio n upon the bacteria. Its germicide action on the bacteria shou ld be so strongthat a dose which wou ld be fatal or very inj u riou sto them wou ld be too smal l to have a deleteriou sinfluence on the body of the indivi dual . I t hasnot proved an easy task to di scover d rugs whichwi l l have any value as germicides when used inquanti tie s so smal l as to produce n o in j uriou se ffect on the body .

A second di fficu l ty i s in getting the drug toproduce its effect at the right poin t . A few

diseases,as we have noticed

,are produced by

bacte ria which d istribute themselves almostindiscriminate ly over the body ; bu t the majo ri tyare somewhat definitely local i zed in specia lpo in ts . Tubercu losi s may attack a single glando r a single lobe o f the l ung. Typhoid germ islocal i zed i n the in testines

,l i ver

,spleen

,etc .

Even i f i t were possible to find some drug whichwou ld have a very specific effect upon the tuberculo sis baci l l us

,i t i s p lain that i t wou ld be a very

questionable method of procedure to i n troducethi s in to the whole system simply that i t mighthave an effect upon a very smal l i so lated gland .

Sometimes such a bacterial affection may be localiz ed i n p laces where i t can be special ly treated

,as

in the case of an attack on a dermal gland,and in

these cases some of the germicides have proved tobe of much value . Indeed

,the use of variou s dis

i nfectants connected with abscesses and superficial i n fections has proved of much value . Toth is extent

,i n disin fecting wounds and as a local

application,the deve lopmen t of our knowledge

of disin fectants has given no li ttle aid to curati vemedicine .

Very li tt le success,however

,has resu l ted in the


which they p roduce are poison s to them as wel las to the individual in which they grow

,and

after these have become qu i te abundan t the fu rther growth o f the bacterium is checked andfinal ly stopped . Part ly

,also

,must we conclude

that these hosti le condi tion s are produced byactive vi tal powers in the body of the indiv idu alattacked . The indiv idual

,as we have seen

,i n

some cases develops a quanti ty of some substancewhich neu tral i zes the bacteria l poison s and thu spreven ts their having thei r maximum effect . Thu srel ieved from the di rect effects o f the po isons

,the

resi sting powers are recuperated and once morebegin to produce a direct destruction of the bacteria. Possibly the bacteria

,being now weakened

by the presence of thei r own products of growth,

more readi ly y i eld to the resi st ing forces of thecel l l i fe of the body . Possibly the resi sting forcesare decided ly i ncreased by the reactive e ffect ofthe bacteria and thei r poisons. But, at al l events,i n cases where recovery from parasi tic diseasesoccurs

,the revived powers of resi stance fina l ly

overcome the bacteria,destroy them o r drive

them o ff,and the body recovers .

Al l this is,of cou rse

,a natu ral process . The

recovery from a disease produced by the in vasionof parasi tic bacteri a depends upon whether thebody can resi st the bacteria l poisons long eno ughfo r the recuperation of i ts resist ing powers . I fthese po isons are very v io len t and produced rapid ly

,death wi l l probably occu r before the resi sting

powers are strong enough to drive O ff the bacteria .

In the case o f some diseases the po isons are sovio lent that th is practical ly always occu rs

,reco v

ery bei ng very exceptional . The po ison producedby the tetanus baci l l u s is of this natu re

,and reco v


cry from lockjaw is of the rarest occu rrence . But

in many other diseases the body is able to wi thstand the poison

,and later to recover its resisting

powers sufficien tly to dri ve o fl'

the i nvaders . Inal l cases

,however, the process i s a natural one and

dependent upon the vi tal acti vi ty of the body . I ti s based at the fo undation , doubtless, upon thepowers o f the body cel ls, ei ther the phagocytesor o ther acti ve cel l s . The body has

,i n short, i ts

own forces for repel l ing invasions,and upon these

forces must we depend fo r the power to producerecovery.

I t is eviden t that al l these facts give u s veryl i tt le encouragemen t that we shal l ever be ableto cure di seases di rect ly by means o f drugs todestroy bacteria

,bu t

,on the contrary

,that we

must ever depend upon the resi st ing powers ofthe body . They teach us

,moreover

,along what

l in e we must look fo r the future developmen to f cu rative medicine . I t i s eviden t that scien

t ific medicine must tu rn i ts atten tio n towardthe strengthening and stimulating of the resisting and curat ive fo rces of the body. I t mustbe the physician ’s aimto enable the body to t e

sist the po isons as wel l as possib le and to stimulate i t to re - enforce its resistant forces . Drugshave a place in medicine

,o f course

,bu t thi s p lace

i s chiefly to stimu late the body to react againsti ts i nvading hosts . They are

,as a ru le

,no t spe~

cific against defin ite diseases . We can not hopefor much in the way of discovering special medicines adapted to special diseases . We must simply look upon them as means which the physicianhas i n hand for stimu lating the natu ral fo rces ofthe body, and these may doubt less vary wi th di fferen t i ndividual natures. Recognising this, we

1 90 T HE ST ORY O F G ERM L IFE .

can see also the lo gic o f the smal l dose as compared t o the large do se . A small dose o f adrug may serve as a stimu lan t fo r the laggingforces, whi le a larger dose wou ld d irect ly repressthem or p roduce i nj u r iou s secondary effects. Assoon as we recognise that the aim of medicine isnot to destroy the disease but rather to st imulatethe resi st ing fo rces of the body

,the who le logic

o f therapeutics assumes a new asp’

ect .Physicians have understood this

,and

,espe

cially i n recent years, have guided thei r practiceby i t . If a moderate dose of quin ine wi l l checkmalaria i n a few days

,i t does n o t fo l low that

twice the dose wi l l do i t i n hal f the time or withtwice the certainty . The larger doses o f thepast

,i ntended to drive out the disease

,have been

everywhere replaced by smaller doses design edto stimulate the lagging body powers . The modern physician makes no attempt to cure typhoidfever

,hav ing long since learned his inabi l i ty to

do this,at least i f the fever on ce gets a foothold ;

but he turn s hi s attention to every conceivablemean s of increasing the body ’s strength to resistthe typhoid poison , confiden t that i f he can thusenable the patien t to resi st the poi son ing effectso f the typhotoxine hi s patien t wi l l i n the end t e

act against the disease and drive o ff the invadingbacteria . The physician ’s duty i s to watch andguard

,bu t he must depend upon the vital powers

of his patien t to carry on alone the actual batt lewith the bacterial invaders.

ANT IT OXINES .

I n very recent times,however

,our bacterio lo

gists have been pointing out to the world certain


diph theria baci l l u s . This po i son i s easi ly o b

tain ed by causing the diphtheria baci l l us to growi n common media i n the laboratory for a whi le

,

and the tox ines develop i n quan tity ; then , byproper fi l tration

,the bacteria themselves can be

removed,leaving a pure so lution o f the toxi c

poison . Smal l quanti ties of this poison are in o culated into the horse at successive in terval s . Theeffect on the horse i s the same as i f the an imalhad the di sease . I ts cel ls react and produce aconsiderable quanti ty of the antitox in e whichremain s i n so lution in the blood o f the animal .This i s no t theo ry

,bu t demonstrated fact . The

blood of a horse so treated i s found to have theeffec t of neu tral i z ing the diphtheria po ison

,al

though the blood o f the horse before such treatmen t has n o such effect. Thus there i s developedin the horse ’s blo o d a quanti ty of the anti toxine

,

and now i t may be u sed by physicians whereneeded . If some of thi s horse

’

s blood , properlytreated

,be inocu lated in to the body of a person

who i s su ffering from diphtheria, i ts effect , provided the theo ry o f anti tox ines i s t rue, wi l l be tocounteract in part

,at least

,the poisons which are

being produced in the patien t by the diphtheriabaci l l u s . This does not cure the disease no r ini tsel f drive o ff the baci l l i

,but i t does protect the

body from the poison s to such an extent as toenable i t more readi ly to assert i ts own resi stingpowers.This method of using anti toxines as a help in

curing disease i s very recen t,and we can not even

guess what may come of i t. It has apparent lybeen successful ly appl ied in diph theria. I t hasalso been used i n tetanus wi th sl ight success .The same pri nciple has been used in obtaining an


antidote for the poison of snake b i tes,since i t has

appeared that i n th i s kind of poison ing the bodywi l l develop an antidote to the poison i f i t gets achance . Horses have been treated in the sameway as with the diphtheria poison

,and in the

same way they develop a substance which neutraliz es the snake poison . Other diseases arebeing studied to - day with the hope of simi larresu l ts. H o w much further the principle wi l l gowe can not say

,nor can we be very confident that

the same principle wi l l apply very widely . Theparasit ic diseases are so differen t i n natu re thatwe can hardly expect that a method which is satisfactory in meeting one of the diseases wi l l be verylikely to be adapted to another . Vaccination hasproved o f value i n smal lpox

,but i s n o t of u se i n

other human diseases. Inocu lation wi th weakened germs has proved of valu e in anthrax andfowl cholera

,bu t wil l no t apply to al l di seases .

Each of these parasites must be fought by specia lmethods

,and we must no t expect that a method

that is of value in one case must necessari ly beof use elsewhere . Above al l

,we must remember

that the anti tox ines do no t cure in themselves ;they on ly guard the . b o dy from the weaken ingeffects O f the poisons unti l i t can cure itse l f

,and

,

unless the body has resisting powers,the anti

tox ine wi l l fai l to produce the desi red resu lts .One fu rther po in t in the action of the anti

toxines must be noticed . As we have seen,a

recovery from an attack o f most germ diseasesrenders the individual for a time immune againsta second attack . This applies less

,however

,to a

recovery after the art ificial'

in o culat io n with antitox ine than when the indiv idual recovers withou tsuch aid If the i ndividual recovers qui te inde


penden tly of the artificial an ti toxine , he does so

in part because he has developed the anti toxinesfo r counteracting the po i son by hi s own powers.His cel l u lar activi ties have

,i n other words

,been

for a moment at least tu rned in the direction ofproduction of an ti toxines . I t i s to be expected

,

therefore,that after the recovery they wi l l sti l l

have thi s power, and so long as they possess i tthe indiv idual wi l l have protection from a secondattack . When , however, the recovery resu lts fromthe artificial inocu lation of an ti tox ine the bodycel ls have not acti vely produced anti tox ine . Theneutral i zation of the poison s has been a passiveone , and after recovery the body cel ls are nomore engaged in producing anti toxine than before . The anti toxine which was inocu lated i ssoon el iminated by secretion

,and the body i s

left with practical ly the same l iabi l i ty to attackas before. I ts immunity i s decidedly fleeting

,

since i t was dependent not upon any activi ty o nthe part of the body

,bu t upon an artificial in o cu

lation of a materia l which is rapid ly e l iminatedby secretion .

C ONC L USION .

I t i s hoped that the out l ine which has beengiven of the bacteria l l i fe of Natu re may serve togive some adequate idea of these organ isms andcorrect the erroneou s impressions in regard tothemwhich are wide ly prevalent . I t wi l l be seenthat

,as our friends

,bacteria p lay a vastly more

important part in Nature than they do as ou renemies . These plan ts are minute and ex trao r

dinarily simple , but , nevertheless, there ex i sts alarge number of different species. The number

1 96 THE ST ORY OF GERM L IFE.

the prematu re death o f an individual ; once in a

whi le,i ndeed

,they may sweep o ff a hundred or a

thousand indiv idual s ; but it i s equal ly t rue thatwithou t them plan t and animal l i fe wou ld be impossib l e o n the face of the earth.

1 98

I .Indigo , preparatio n o f , 57.

Inflammatio n in surge ry , 1 53 .

In ternal structure o f bacteria, 30 .

Invasio n , means o f , 1 45 , 1 69 .

J .

Jute , 44.

K .

Ko ch, co n tributio n to bacterio lo gy ,1 6.

L actic acid, 55 .

L eather, 46.

L eeuwenho ek, studies o f , 10 .

L e mes in nitro gen fixatio n , 1 08 .

L ie.

ig, theo ry o f fermen tatio n , 1 3 .

L imits o f pre ven tive medicine , 1 82 .

L inen , 42 .

L o ckjaw , 1 3 5 .

L y smes, 1 5 1 .

M.

Maceratio n industries, 42 .

Maceratio n o f skele to ns, 46.Malaria, 160 .

Malignan t pustule , 1 7.Micro be , definitio n 0 9.

icro co ccus, defined, 1 8 .

Milfl"bacteria, so urces o f , 67 ; growth

0 70 .

Milk, eflect o f bacteria o n , 70.

Milk handling, 74.Mo tio n o f bacteria, 28.Muller studies o f , 1 1 .

Multiplicatio n , rapidity o f , 2 1 .

My coderma ace ti, 52.

N.

Nitrate beds, 1 16Nitrify ing bacteria, 10 3 .

Nitro gen fixatio n , 107.Nitrogen lo ss, 1 04.

O .

O pium,.

63 .

O scillame , as allies o f bacteria, 3 2 .

P.

Parasitic bacteria“3 4.

Pasteur, co n tribut io ns o f , 14.

INDEX.

Pathogenic bacteria, abundance o f,1 29.

Patho gen ic bacteria n o t true para

sites, 1 3 1 .

Phago cy tes , 1 5 1 .

Po iso ns produced by bacteria, 1 30 ,1 3 2 .

Pre ven tive in o culatio n ,Preven tive medicine , 1 66 limi ts o f ,1 82 .

Products o f bacterial life , 41 , 47.ure cultures, 1 5 ; In Vinegar making, 5 1 in

o

to bacco curing, 61 in

hu t termaking, 82 In cheesemaklng t 93 °

Pus,1 5 3 ; pus co cci, 142 .

R.

Reco ve fromgermdiseases, 1 56.

Redmil 72 .

Resistan ce to disease, 147.

T .

T ain tedmilk, 72 .

T e tanus, 1 3 5 .

T o bacco curing, 58 .

T ro ublesome fermentatio ns, 63 , 1 2 1 .T uberculo sis, 1 3 6.

T y pho id fever, 1 3 6.

S.

Sarcina. defined, 1 9.

Sauer Kraut 65 .

Scavengers , bacteria as , 95 , 1 0 1 .

Schwann ,studies o n fermen tatio n ,

1 2 .

Seeds, s ro uting o f , 1 1 1 .

hape 0 bacteria, 1 7.

ilo , bacteria in ,1 1 2.

ize o f bacteria, 1 7 .

kele to ns 46.

lim milk, 72 .

nu pre

paratio n o f. 59.

So apy mil 72 .

So il, fertility o f , 1 14.

So urces o f in fectio us material, 168 .

So un ng o f milk, 70 .

Species, differences be tween , 2 3 , 3 4 ;names o f , 3 7.

Spo nges. 4s.

Spo res, 25 .

Staphy lo co ccus py o genes, 142 .

Strepto co ccus, defined, 1 9.

Strepto co ccus py ogenes, 1 42.Surgery, bacten am, 1 7 1

Suscept ibility o f the individual, 145 .

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T his bo o k o ught to be in every divinity scho o l in whichman as wellas G o d is studied, an i fromwhichmissio naries go o ut to co nvert the humanbeing o f reality and n o t the man o f rhe to ric and tex t - bo o ks.

—Bo sto nL iterary Wartd.

T HE BE GINNING S OF WRI T ING . By W. J.

HO FFMAN, M. D. With numero us Illustratio ns. 1 2mo .

C lo th,

T his in tere stingbo ok gives amo st attractive acco unt o f the r ude metho dsemplo y ed by primrtive man fo r reco rding his deeds. T he earliest writin

co nsists o f picto graphs which were traced o n sto n e , wo od, bo ne , skin s, anvario us paperlike substances. Dr. Ho fi

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man sho ws ho w the several classes

o f symbo ls used in these reco rds are to be interpreted, and traces the gro w tho f co n ven tio nal signs up to sy llabaries and alphabe ts—the two classes o fsigns emplo y edby mo dern peo ples.

IN PREPARAT ION.

THE S O U TH SEA ISL ANDERS . By Dr. SC HMEL T Z .

THE Z UNI . By FRANK HAmL T ON C USHING .

THE AZ TE C S . By Mrs. ZEL 1A NUT T AL L .

D. APPL ET ON AND C OMPANY, NEW YORK.

D. APPL E T ON AND C O MPANY’S PUBL IC AT IO NS .

APPL ET ONS’ L IBRARY L IST S.

L ibraries, whether fo r the scho o l. home, o r the publicamo ng the mo st im rtant and wide- reaching educa tio naladvancemen t o f civ

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izatio n . Modern in tellectual activity , keeping pacewithmodern inventio n , has added to the

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w lier sto nes o f literature m dso f bo o ks, and a still

glreatermass o f readingmatter in o ther fo rms. nfo r

tunately , much o f t e material put in to prin t is no t o f an edueatio nal o relevating character. It h impo rtan t, the n , in the selectio n o f bo o ks fo rpublicuse, especial! fo r the y o u

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r

v

r

igl, that great care be exercised to secure o nly

such kinds 0 reading as be who lesome, instructive, and intrinsicallyvaluable .

Fo rmo re than fifty years Messrs .

.

D° Appleto n andC ompany have beenengaged in the publica ti o n o f the cho ro est productio ns fi

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omthe pens o f distrn urshed autho rs o f the past a nd presen t, o f bo th Euro pe and America,an their catalo gue o f bo o ks n ow comprises se veral tho usand vo lumes embracing every departmen t o f kn o w ledg

. C lassified lists o f these publicatio ns have been prepared, afi rrding cilities fo r a judicio us selectio n o fbo o ks co vering the who le range o f L iterature, Sa

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enee, and Art, fo r individual bo o k buy ers o r fo r a tho ro ugh equipmen t o f an y library .

L isrs A, B, and C are o f bo o ks selected especially fo r Scho o l L ibraries .

L ist A .—Fo r Primary and In termediate Grades .

L i ft B .—Fo r Grammar and H zg

'lr Sebo o l Grades .

L ist C .—For C o llege and Un iversity L ibraries.

The o ther lists are o f bo o ks gro uped acco rding to subjects, and include

T he classificatio ns are as fo llows

L ist D.—Histo ry . L ist 0.

—Language, L iterature , andE—Bio graphy . Art .F.—Phy sical Science . P.

—Reference Bo oks .

G .—Men tal and Mo ral Science . Q .

—Po e try and Essay .

H .—Po litical andSo cial Science. R.

—T ravel and Adventure .

I—Finance and Eco nomics. S.- Pedago gy andEducatio n.

K.—Hy giene and Sanitary Sc: T .

—Fictio n .

ence . U.—Amusemen t and Recrea

L .—Philo so phy and Me taphy s tio n.

ics. V.—Evo lutio n .

M.—T echno lo gy and Indus W.

—Religio n .

trial Arts. X.—L aw.

N.—An thro po lo gy , Ethn o lo gy , Y .

—Medicine .

Archaeo lo gy , Pale o n to l Z .—Juvemle Bo o ks .

o gy .

AA.—Unclassified. BB.

—Scho o l and C o llege T ext -Bo o ks.C C .—Span ish Publicatio ns.

‘Ve respectfully invite the atten tio n o f public and private bo o k buy erseverywhere to these lists, co nfiden t that they w ill be fo und o f interest and

pro fit. Single lis tsmailed free . C omplete set, 1 8 cen ts, to co ver po stage.

D. APPL ET ON AND C OMPANY,NEW YORK.

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