2OQ 



bility, the result of breeding, and, therefore, of inheritance. 

 By this I do not mean that the parents or ancestors 

 must necessarily have undergone attacks of acute infectious 

 diseases, or that they possessed a similar predisposition or 

 insusceptibility towards them, but that somehow these 

 predispositions and insusceptibilities have appeared as 

 constitutional peculiarities, and that they have constituted a 

 life-heritage just as much as any other constitutional 

 peculiarity which they may have obviously inherited. 



Heredity preserves the race by varying the individual, and 

 the law of variability, known only by its effects, is respon- 

 sible for this individual differentiation ; but how these 

 effects are produced we cannot tell, for "as one star differeth 

 from another," so does every individual, not only in what 

 he acquires, but still more in what he inherits, and further 

 we cannot go. It is therefore unnecessary that I should 

 go into any detail in considering the remaining affections in 

 this group viz., dysentery, yellow fever, the plague, dengue, 

 miliary fever, influenza, hay fever, (undoubtedly hereditary), 

 epidemic cerebro-spinal meningitis, and whooping-cough. 

 That they are all produced by external causes introduced 

 into the system is an admitted fact, but that, in relation to 

 each one of them, some individuals are particularly pre- 

 disposed, while others are comparatively insusceptible must 

 also be admitted. That both this predisposition and in- 

 susceptibility may be inherited, i.e., the result of inheritance, 

 using the term in its broadest signification, admits but of 

 little doubt, and this is all I contend for. For although the 

 effects of the acute specific or infectious diseases leave no 

 trace in the affected tissues that can be transmitted to any 

 extent, yet it must be conceded that far beyond the agency 

 of external circumstances, and the relative immunity pro 



