HEREDITY AND DISEASE 11 .'i 



upon social as well as individual practice. If it 

 could be demonstrated, for instance, that the sus- 

 ceptibility to certain grave diseases is confined to 

 certain members of the community, who inevitably 

 transmit it to their children, we might well regard 

 it as a duty to interfere with the reproduction of 

 those persons — as would the disease itself, in accord- 

 ance with the law of natural selection. 



In the third place, it is of importance to consider 

 whether susceptibility to a disease acquired -by an 

 individual can be transmitted to his otispring as an 

 actual part of the germinal inheritance. But, in brief, 

 it may be said that the study of heritability of disease 

 does not reveal any exceptions to the laws of heredity 

 observed in normal cases. 



Having excluded so many familiar cases as not 

 properly to be called facts of inheritance, let us 

 now consider the true cases of the inheritance of 

 disease. 



And, first of all, let us note the existence of certain 

 nervous abnormalities which are inherited. Merely 

 mentioning the peculiar case of FricdreicJis or 

 Hereditary ataxia, which is usually seen in several 

 children of one family, and is certainly of germinal 

 origin, but is not found in their parents, we may 

 say that definite nervous disordia-s are not inherited, 

 but that various disorders may arise in consequence 

 of the inheritance of an instability or tendency to 

 disease of the nervous system. Dipsomania, for 

 instance, is not inherited ; but the state of the 

 nervous system which leads to dipsomania in the 

 father may often be transmitted to his son. If, 

 however, the alcoholic habit is acquired as the result 



II 



