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HEREDITY IN MENTAL AND NERVOUSDISEASE.

HEREDITY IN MENTAL AND NERVOUS DISEASE.

THE LANCET.

LONDON: SATURDAY, MAY 16, 1925.

THE transmission from parent to offspring of s

mental and physical characteristics has been accepted (

as a fact from the beginning of time, but this principle fcannot be applied to disease processes quite so simply. (

The complex living organism is made up of a number i

of individual entities together composing the whole, 7and in the consideration of the transmission of 1

qualities the questions at once arise: Does the innatecharacteristic of the individual persist unchanged andis it transmitted in its unchanged form, or can thecharacteristic be modified during the life of the iindividual, and can this modified characteristic betransmitted ? The Mendelian laws showed that incomparatively simple organisms, with clearly recognis-able traits, the innate characteristic persisted and thatthe manner of its appearance in the progeny could bemathematically computed. The advent of Darwinismand the theory of sporadic variation further deflectedattention from the second possibility, but opinion nowshows a trend towards the neo-Lamarckian attitudewhich affirms that the acquired modification may,under suitable circumstances, be passed on. TheMendelian law is very hard to apply in the complexorganism and more particularly in the field of disease.It is difficult, in the first place, to pick out the definitefundamental trait, the unit characteristic ; whatappears unitary may, in fact, prove to be highlycomplex. Apart from a very limited group ofabnormalities, such as haemophilia, albinism, andcertain familial myopathies, very little in this line hasactually been accomplished beyorid the establishmentof a certain persistence of characteristic in a family tree.

In medicine it has been the custom to introduce theheredity as an aetiological factor in disease, especiallyin cases where no other definite causative factor isknown. The history of pathological research, however,offers many instances where the hereditary influencewas once supposed to be the all-important agent, whenfurther advances in knowledge have shown the diseaseto be one acquired in the life-time of the individual.In such cases, even where the disorder has been

definitely proved to be due to an environmental cause,such as the invasion of micro-organisms, the exponentsof the hereditary theory merely change their groundand speak of a

" diathesis " or a "constitutionaltendency." Prof. ABRAHAM MYERSON, in a workreviewed in our columns this week, emphasises thispoint in relation to tuberculosis. He says:

" Up till Trudeau’s time, in fact right up to thediscovery of the tubercle bacillus by Koch, the mainfactor in the causation of the disease was held tobe heredity. There were plenty of families foundin which tuberculosis occurred generation aftergeneration,’ plenty of families found in which allor many of the brothers and sisters had the disease,the same kind of evidence we have to-day for the’inheritance of insanity.’ ... With the discovery ofthe infecting organism as a cause of tuberculosisheredity received a knock-out punch; in fact,everyone now loudly proclaims that there is noheredity in tuberculosis, but instead the meta- I

physical predisposition’ is acclaimed, and stilllingers to obfuscate intelligent thinking." I

The real obstacle, as it appears to us, in the wayof any advance in our knowledge of the hereditarytransmission of disease lies, firstly, in the difficultyof finding a " unit character." There are few diseaseswhich can be so regarded ; the majority are

symptomatic groupings. Particularly does this applyto mental and nervous disorder, of whose ultimatenature we have at present little accurate knowledgeand concerning which it is probable that futureresearch will radically alter our conceptions. Secondly,we do not know how far a certain grouping of

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symptoms may constitute a biological reaction tocertain specific environmental circumstances. Because

) a certain symptom-complex appears in a national.

or family grouping it does not necessarily follow thatthe cause lies within. There is a strong measure of, probability in the alternative explanation-viz., thatE the mechanism of biological adaptation to the environ-ment is producing a similar series of reactions in a

( number of individuals exposed to the same conditions.3Thirdly, we are remarkably ignorant of the laws3governing degeneracy, atavism, or simple failure of3 development. It is a matter of consideration whether1 a number of the disease entities now recognised are- not phenomena of this order rather than diseaset processes proper.B The progress of homo sapiens has been not biological1 but sociological ; it has depended upon his control ofi and ability to grow at the expense of his environment.v The development of man is not reckoned in terms ofe biology but in terms of his capacity for using materials, -the Stone Age, the Bronze Age, the Age of Steam.e There has been steady progress in the manipulation ofx the environmental factor, and it may be that the;. hope of medical science lies in a further extension ofe this principle. It is a comforting reflection that the,t history of medicine shows a steady tendency to

y eliminate the hereditary in favour of the environmentalþf cause as the knowledge of morbid processes has becomed more explicit. For it is still a question whether thes advance of the human race depends upon the adapt-Lt ability of man to his environment or upon his capacity3. for adapting the environment to himself.le

THE DYNAMICS OF THE CELL.IN man’s scientific struggle to bring under his direct

control all the reactive phenomena exhibited by theanimate and inanimate world, progress has beenconditioned to a large extent by his power of analysingthe concrete basis of his research into particles of everincreasingly minute dimensions, and of defining thelaws governing their mutual interaction. Physics andchemistry are approaching each other on the commonground of atomic and molecular dynamics. Physio-logy, towards which medicine must unceasingly lookfor a rational interpretation of the problems whichconfront her, is on her part largely dependent, andultimately entirely so, on the physico-chemicalelucidation of the structure of matter. Without in theleast wishing to disparage experimental work done onthe whole animal and especially on man-work to

, which physiology and medicine owe a great and

lasting debt-we cannot refrain from emphasising the, tendency at present exhibited in physiology to make: use of the synthetic method of experimentation., Such a method of study-namely, the study of the

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functions of an organ isolated from the disturbing and: uncontrollable influences of the rest of the body-. enables a much more exact determination of theL reaction of the individual organ to changes in environ-ment to be made than would otherwise be possible.