302 HEREDITY AND DISEASE 



natural inheritance does not promote cheerfulness, yet there 

 can be little doubt that the oppressiveness of the facts is com- 

 monly exaggerated — especially by those who do not trouble 

 themselves to think out the business clearly, 



A medical authority (quoted by F. Martins, 1905) goes the 

 length of saying, " For the practitioner the concept of heredity 

 is quite useless, and he should not deal with it at aU. What 

 is wrought out during the life of the individual can be dealt 

 with. What is due to the parents is unalterable." 



This is an extreme expression of the practical pessimism which 

 many feel. We cannot choose our parents ; we cannot refuse 

 our legacy. The Ethiopian cannot change his skin, or the 

 leopard his spots. 



But this extreme pessimism is unwarranted. The fact is that, 

 if " the inheritance of disease " really occurred to the extent 

 and in the manner many medical writers assume with so much 

 conviction, the human race would have been extinct long ago, 

 or in any case we could not now have the broad and strong 

 stream of healthfulness which, in spite of all disease, still surges 

 around us. 



Let us look for a little at the more hopeful aspects of the 

 question : 



(i) As regards microbic diseases, a predisposition to which 

 may be inherited, the progress of hygiene and preventive medicine 

 tends increasingly to diminish the risks of infection or of fatal 

 infection. 



(2) There is some reason to believe that, in regard to some 

 microbic diseases, a relative constitutional immunity is in 

 process of evolution. 



(3) There is no scientific warrant for believing that acquired 

 diseases — i.e. those arising as modifications from without, to 

 which there is no specific predisposition — are as such trans- 

 missible. By liberating toxins and the like in the body, or by 

 depressing the general nutrition, acquired diseases may pre- 



