NERVOUS DISEASES 263 



Nervous Diseases. In regard to so-called "acquired nervous 

 diseases," I venture to quote again from the. late Professor 

 D. J. Hamilton (1900, p. 299): " Have we crucial evidence to 

 show that a mental disease may be excited through external 

 agencies, as, for instance, by the abuse of alcohol in a person 

 free from any ancestral taint, and that this disease so excited 

 can be transmitted through several generations ? My own 

 impression is that we have not. ... So far as I am personally 

 informed, I feel that, in mental derangement, and in excess of 

 perhaps any other form of disease, we have to do with an 

 inherited peculiarity or variation a variation which may have 

 occurred in a far-back ancestor and lain dormant for many 

 generations, but which inevitably manifests itself under con- 

 ditions of unusual external stimulation, and which is in no 

 respect bound up etiologically with or necessitated by this 

 stimulus. The substratum which underlies the mental pecu- 

 liarity is allied to that-underlying the predisposition to tuber- 

 culosis or gout, and, probably, is referable to a fault in metabolism 

 excited, it may be, by an inherent bias towards degeneration in 

 the nerve-cells of the brain, and this is eminently hereditary." 



The general verdict of those experts who admit the validity 

 of the distinction between endogenous germinal variations 

 and exogenous somatic modifications may be thus summed up : 

 (i) externally induced nervous disorders (apart from the 

 results of wounds and wholesale poisoning of the system) are 

 extremely rare in persons free from ancestral taint ; (2) here- 

 ditary transmission in such cases is quite unproved, if we discount 

 cases where the whole system of the parent (including the 

 germ-cells) is poisoned by alcohol, opium, or the like. 



In short, whenever a disease has been acquired, when there 

 is no specific predisposition towards it, when it is in biological 

 terminology modificational, it seems unlikely that there will 

 be any specific hereditary effect on the offspring. The most that 

 can be admitted is that very virulent acquired disease may io 



