THE CAUSATION OF DISEASE. 325 



the rnal-E attaching to many occupations, and in such cases S 

 is in no way responsible for the mal-E ; nevertheless, there 

 are manifold mal-E's at hand, which the individual may court 

 or shun at his pleasure, such as drink and other excesses ; 

 and the tendency to indulge in these is inherited. It is 

 generally acknowledged, for instance, that such is the case with 

 intemperance ; and thus a man may inherit cirrhosis of the liver, 

 not through any very special tendency of that organ to 

 undergo morbid change, but through an inherited tendency on 

 his part to expose himself to an E which has the power of 

 calling forth this particular disease. 



Let us now inquire into some of the reasons which have led 

 medical men to under-estimate the share taken by heredity in 

 the causation of disease. 



1. It is quite obvious from the above remarks that an in- 

 dividual may suffer from a hereditary disease, even though none 

 of his progenitors have ever contracted it. We have seen that 

 measles is quite as hereditary as phthisis ; but there are, I 

 take it, isolated tribes of men existing in remote corners of the 

 earth where the measles bacillus has never spread, who yet 

 would be highly susceptible to the poison if exposed to it.* Such 

 would, if attacked, inherit the disease in the strictest sense, 

 notwithstanding the immunity of their ancestors. From this 

 conclusion there is no escape if we grant that the inheritance in 

 measles, as in tubercle, is an inheritance of soil, for exactly the 

 same argument applies to tubercle. There are, I presume, 

 some parts of the world where " consumption " has never yet 

 ravaged, but where the inhabitants, even though free from 

 a " tubercular history," are susceptible enough to the dis- 

 order — quite as susceptible, perhaps, as what would be termed 

 a phthisical family. It is well known that negroes are pecu- 

 liarly apt to suffer from phthisis when they come to this country, 

 and we should probably not be beside the mark if we said of 

 some of them, at all events, that none of their ancestors had 

 suffered from phthisis, and the same remarks apply to monkeys. 



How comes it that the hereditary element is in such cases 



* Before the Fiji Islands were placed under English protection, measles teas 

 unknown there, but shortly after intercourse with the English the disease 

 broke out in a malignant form. 



Z 



