THE PRESENT EVOLUTION OP MAN — PHYSICAL 245 



diathesis is conveyed from parent to child. Unless, 

 then, a distinction be assumed between constitutional 

 consumption and consumption induced by unwhole- 

 some conditions — unless it be asserted that consumption 

 of unknown origin is transmissible, while functionally 

 produced consumption is not, it must be admitted that 

 those changes of structure from which the consumptive 

 diathesis results, may be caused in the parent by 

 changes of function, and may be inherited by their 

 children." — Principles of Biology, vol. i. p. 250. 



Certain modes of life certainly tend to engender gout 

 in those predisposed to it, who in general are the 

 children of parents with similar tendencies. But gout 

 is certainly not transmissible; only the inborn tend- 

 ency to acquire it anew under fit conditions is trans- 

 missible. The offspring of gouty persons are never 

 born with the structural changes which gout has caused 

 in the parent reproduced in them, nor in the absence of 

 the disease do they reproduce them in after life ; but 

 being of similar tendencies they may, under similar 

 conditions — i. e. when suffering from the disease — 

 undergo similar changes. Here, therefore, we have no 

 true instance of the transmission of an acquired trait. 

 Again, it is not true that consumption may be produced 

 in persons previously healthy by unfavourable con- 

 ditions, " by bad and insufficient food, by foul, damp, 

 and unventilated habitations, and even by long-con- 

 tinued anxiety"; and it is never, at the present day, 

 a disease of unknown origin. It is always produced by 

 a particular species of pathogenic micro-organism, the 

 bacillus tuberculosis, which, under conditions that lower 

 the vitality, that reduce the personal vigour of the phago- 

 cytes, attacks even persons normally resistant to it ; in 

 the absence of it no conditions, however unfavourable, 

 can ever produce consumption even in the least resistant. 



