diathesis is conveyed from parent to child. Unless, then, a distinction be assumed between constitutional consumption and consumption induced by unwholesome 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 tendency to acquire it anew under fit conditions is transmissible. 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 conditions, "by bad and insufficient food, by foul, damp, and unventilated habitations, and even by long-continued 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 phagocytes, 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.
