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change, and I have now to mention it inconnexion with the latter, the intensity ofthe light being dependent upon the densityof the substance and the elevation of tem-

perature, but the state of any body whenincondescent is not well understood. Theimmense difference of temperature requiredfor the ignition or different substances is

easily seen by some simple experiments.If I hold a piece of platinum wire in theflame of a spirit lamp, it exhibits a greaterbrilliancy of light than the flame itself, andthat arises from the greater density of the z,

wire ; at the same time it must be under-stood, that there is no one substance whichmay not become luminous on a proper ele-vation of the temperature. The definitionof flame, as given by Sir Isaac Newton, wasthat which accords with our present know-ledge of it, namely, "that it is ignited va-pour." Now, here you may observe a flamearising from a jet of hydrogen gas, whichis scarcely visible, which shows us thatflame may exist without any solid sub-stance,-it is therefore ignited vapour; andthat it possesses a considerable degree ofheat, may be seen from its power of heat-ing platinum wire to a great state of incon-descence. But generally speaking, in theflame of a candle or lamp, it is the charcoallioerated by the decomposition of tne mate-rial employed, which gives a body to theflame, which is the chief substance of ig-nition. If you apply a cold substance overa flame, or especially if we hold a wiregauze over a flame, we extinguish a portionof the flame, because we co(,l it, the wiregauze being an excellent conductor and ra-diator of heat, and that the cooled gaseous 1matter passes through, may be seen by againlighting it upon its upper surface. Theflame of phosphorus is, as you know, ex-ceedingly bright, which depends merely on Ithe circumstance, that the flame of phos- iphorus is a solid substance, whereas thecombustion of matter generally is in a stateof vapour. The experiment was made ofholding a wire gauze over the flame of

phosphorus, and sufficient phosphoruspassed through the wire to support combus-tion again on the opposite side when kin-dled. The discovery of these facts respect-ing the nature and properties of flame, ledSir H. Davy to apply them to the construc-tion of that valuable contrivance, the miners’sajèty lamp, which will be explained whenwe have to consider the properties of carbu-retted hydrogen gas.

In the next Lecture, Mr. Brande willcommence the description of the simple szcp-pOt’tO’S of combustion.

FOREIGN DEPARTMENT.

ON THE MODUS OPERANDI OF ALOES, ANDITS MEDICAL PROPERTIES.

BY DR. WEDEKIND.

IT is well accertained that the purgativeeffect of aloes does not take place till eightand sometimes twelve hours after its exhibition. Individuals in whom the,4ecre-tion of bile is increased with the greatestfacility, are those most powerfully actedupon by aloes. An excitement of the wholesystem, with quickness of the pulse, disa-greeable heat of the abdomen, dryness ofthe mouth, succeeds the administration ofthis remedy. These effects are increasedwhen the medicine is continued during se-veral days, and if exhibited in very strongdoses, it sometimes gives rise to serioushaemorrhages. ,

i From experiments made on persons inhealth, and observations on persons in sick-ness, it has been found that a purgativewhich acts speedily, as, for instance, a mix-ture composed of a laxative infusion andsulphate of soda given at one time, withtwo or four grains of aloes, does not act dif-ferently than if exhibited alone. But aloesgiven two hours before the mixture, doesnot commence to operate till the effect ofthe latter has ceased, and the evacuationsin second purging differ from those in -thefirst, as well as in appearance as in smell.If, on the contrary, the aloes be given fromsix to eight hours before the mixture, theeffects of the two remedies coincide, andthe evacuations are generally very copious.

If the stools produced by the aloes are notwatery, but bilious, faeculent, and have aspecific smell, it is not owing to a specialaction on the large intestines, as authorshave-generally stated. The author of this

paper had several opportunities of tryingthis remedy in icterus ; and as long as thestools were white or grey, aloes did notpurge even when exhibited in large doses;but the purgative effect immediately super-vened, as soon as the faecal matter com-menced to contain bile, a proof that thepresence of bile in the intestinal canal is a

necessary condition of the purgative effectof the aloes. If the aloes were given in toolarge doses, a bilious diarrhoea generallyfollowed.

It is, then, useless to give aloes withneutral salts, and other salts which act

promptly, unless it is desired to promotethe secretion of bile ; and under such circum..stances, the aloes should be given somehours before the Qther medicine. The pan-

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creatic and hepatic secretions will be stillmore increased by the addition of calomel.

It appears, then, that the primitive effectof the aloes is on the liver, that this organ isexcited by it as the salivary glands are bymercury, or the kidneys by cantharides ;that its purgative effect does not depend, asthat of many other cathartics, on an in-creased secretion from the intestinal canal,and an immediate excitement of the muscu-lar fibres of the intestine; but the aloes isfirst absorbed, then carried into the circu-tion, and afterwards secreted by the liver,the action of which it increases.

Dr. Wedekind thinks, that the use ofaloes is principally indicated when thesecretion of bile is scanty, in constipation,from atony of the colon and rectum, and inicterus, which may be attributed to atonyof the liver. This medicine should be em-

ployed with much caution in irritable per-sons. In cases of icterus, attended with aspasmodic or inflammatory state of the liver,obstructions of the liver with dropsy, as

well as in persons affected with biliary cal-culi, and those disposed to haemorrhoids, itsuse is decidedly improper.

INCUBATED EGG.

The various vital processes of nutrition andformation, which are carried on in the foetusof the mammalia while in its mother’s

body, and by means of the most intimateconnexion with the parent, are effected inthe incubated chick by its own powers,quite independently of the mother, andwithout any extraneous, substance, exceptthat of the atmospheric air, and a certaindegree of warmth. The egg is covered,within the shell, by a white and firm mem-brane (membrana albuminis), which containsno blood-vessels. The two layers of thismembrane, which in other parts adhere

closely to each other, leave at the large enda space which is filled with atmospheric air.This membrane includes the two whites of theegg, each of which is surrounded by a deli-cate membrane. The external of these isthe most fluid and transparent, the innerone thicker and more opaque ; they may beseparated in eggs which are boiled hard.The internal white surrounds the yolk,which is contained in a peculiar membranecalled the yolk-bag. From each end of this

proceeds a white knotty body, which ter-minates in a flocculent extremity in thealbumen. These are called the chalazce or

grandines. Leveille distinguishes a thirdwhite, and considers the chalazae as absorb-ing vessels floating in it, and destined toabsorb it as well as the inner albumen, andmix them with the yolk during incubation.A small round milk-white spot, called thetread of the cock (cicatricula or macula) is

formed on the surface of the yolk-bag. Itis surrounded bv one or more whitish con-centric circles (halones or circelli), the useof which, as well as that of the cicatriculaitself, and of the chalazse, is not yet ascer.tained. We now proceed to notice thewonderful successive changes which go cnduring the incubation of the egg ; and themetamorphoses which are observed both inthe general form of the chick, and in pay-ticular viscera. The periods of these changeswill be set down from the hen, as affordingthe most familiar example. It will be bestto give, first, a cursory chronological viewof the whole process, and then to make afew remarks on some of the most importantparts of the subject. A small shining spotof an elongated form, with rounded extre.

mities, but narrowest in the middle, is per.ceived at the end of the first day, not in norupon the cicatricula, but very near thatpart on the yolk-bag (nidus pulli, colliquamerc-tum, areole pellucida). This may be said to

appear before-hand, as the abode of thechick which is to follow. No trace of thelatter can be discerned before the beginningof the second day, and then it has an incur-vated form resembling a gelatinous filament,with large extremities vety closely sur.

rounded by the amnion, which, at first, canscarcely be distinguished from it. Aboutthis time the halones enlarge their circles,but they soon after disappear entirely, as

well as the cicatricula.The nrst appearance of red blood is dls.

cerned on the surface of the yolk-bag, to-

wards the end of the second day. A seriesof points is observed, which form grooves,and these closing, constitute vessels, thetrunks of which become connected to thechick.’ The vascular surface itself is calledfigura venosa, or a1’ca vasculosa, and the vesselby which its margin is defined, vena termi.nalis. The trunk of all the veins joins thevena port2e, while the arteries, which ra-mify on the yolk-bag, arise from the mesen-teric artery of the chick. On the com.mencement of the third day, the newly-formed heat (the primary organ of the cir.culating process which now commences) isdiscerned by means of its triple pulsation,and constitutes a tliree-fold punctum saliens.Some parts of the incubated chicken aredestined to undergo successive alterationsin their form ; and this holds good of theheart in particular. In its first formation itresembles a tortuous canal, and consists ofthree dilations lying close together, and ar-ranged in a triangle. One of these, whichis properly the right, is then the commonauricle ; the other is the only ventricle, butafterwards the left; and the third is the dita-tated part of the aorta (bulbus aorta). Aboutthe same time, the spine, which was ori.ginaDy extended in a straight line, becomes