70 HEREDITY AND SELECTION IN SOCIOLOGY 



due to a general weakening of the constitution of the parents ; 

 and this weakening, this sapping of the constitution, must 

 inevitably react upon and affect the germ-cells, as much as it 

 reacts upon and affects all the somatic cells. Secondly, tuber- 

 culosis has, more than any other disease, a social aspect as well 

 as a biological one. The child who is born of parents whose 

 constitution is undermined by tuberculosis, who is consequently 

 hereditarily weak, is, in the majority of cases, placed in an en- 

 vironment which cannot fail to influence unfavourably and to 

 weaken still further this already weakened constitution ; and thus 

 the child is an easy victim of the tubercle. In a sense, therefore, 

 tuberculosis may be regarded as acquired afresh in each succes- 

 sive generation ; it is not the disease itself which is transmitted, 

 but a certain pathological predisposition due to a weakening of 

 the constitution. That this is really the case— that tuberculosis 

 is, strictly speaking, always acquired, and that the predisposition 

 to its acquirement may be counterbalanced by therapeutic 

 means— is proved by Professor Grancher's experiment in France. 

 He separated children from their tuberculous parents, and 

 removed them to more healthy surroundings, with tolerably 

 successful results. 



The same may be said in regard to cancer. No single case of 

 the actual transmission of a clinical form of cancer has, to our 

 knowledge, been observed, and the inheritance of cancer is 

 now very generally denied altogether. But even were a 

 predisposition to cancer hereditary in the case of children of 

 cancerous parents— which is by no means proved — ^it is obvious 

 that the morbid growth of tissue in the organism, by its 

 usurpation of an abnormal quantity of blood, must react upon 

 the reproductive cells and weaken them to a greater or less 

 degree. 



The transmission of epilepsy has also been urged against 

 Weismann's theory. It must be remarked, however, that the 

 experiments of Brown-Sequard on guinea-pigs, which form the 



