TUBERCULOSIS 285 



with epithelial vulnerability, and in any case, which is all that 

 our argument requires, with a general constitutional peculiarity 

 or germinal variation. 



For the benefit of those who are not satisfied with referring the 

 hereditary predisposition to a germinal variation (though beyond 

 this vagueness it is hardly safe at present for any biologist to ven- 

 ture), we wish to quote again from the late Prof. Hamilton's address 

 on " Heredity in Disease," which marked a distinct step in the 

 discussion of the subject. 



" Where has the inherited strain come from ? What is its 

 ancestral history ? Can it be generated by vicious surroundings ? 

 I question whether it can. No doubt, once in the blood, the par- 

 ticular habit may be fostered by every external agent which tends 

 to deteriorate the natural powers of resistance. But will such 

 external agencies tend to produce a particular colour of hair, a 

 certain narrowness of chest, tallness of stature, and other peculiar- 

 ities which are distinctive of the tubercular constitution ? My 

 conviction is that they will not, and that we must go much further 

 back in the history of the human race to get at the explanation 

 of the matter. My own impression is that these features are the 

 lineal descendants of a variation which took place far back in 

 our history, that the variation has occurred irrespective of sur- 

 roundings or external agencies, and that its influence has been 

 propagated in the descendants ever since. It may be a variation 

 which is common to many race?, but one which apparently is 

 intensely hereditary " (1900, pp. 295-6). It should be noted, 

 however, that this way of looking at the facts is not unanimously 

 accepted. Some experts will hardly admit the inheritance of even 

 the tubercular diathesis as a thing more to be remarked than the 

 disposition to typhoid or diphtheria. The tubercle bacillus is very 

 parasitic, and may bide its time for years, slowly producing, even 

 from a single infected gland, all the appearances of the tubercular 

 type. Moreover it should be remembered that (a) open-air animals 

 rarely suffer from tuberculosis, but surfer at once when confined ; 

 (b) that well-to-do, well-nourished people are much less liable than 

 the poor and ill-fed ; and (c) that phthisis is commonest where 

 overcrowding is greatest, and lessens as hygiene improves. 



In any case, the distinction between the inheritance of a predis- 

 position to a disease and the inheritance of the disease is far from 

 being a quibble about words, as some prejudiced writers still declare. 



