370 



III K AMERICAN NATURALIST 



[Vol. L1V 



however believe in the possibility of a real inheritance of the dis- 

 ease. It is very evident that the discussion has been very much 

 hampered by a confusion of "inherited" and "congenital." 

 And it has seemed to a great many authorities as if the question 

 as to the existence of an inherited moment in tuberculosis could 

 be answered by an investigation into the possibility of pre-natal 

 infection. 



Lastly, there are authors who believe in the inheritance of a 

 certain disposition for tuberculosis. 



From the fact that practically all persons above the age of 

 twelve react positively to von Pirquet's test, it can be seen that 

 tuberculosis infection is not as inevitably the cause of tubercu- 

 losis, as for instance pneumocoecus infection is the cause of' septi- 

 caemia in the mouse. Every practising physician has seen cases 

 in which a joint became tuberculous after a trauma, in a patient 

 who showed no other evidence of a tuberculous infection. But 

 the fact that such cases are rare makes it probable that consti- 

 tutional, genetic, differences in resistance exist between indi- 

 viduals. The same holds true for traumatic carcinoma. 



It is evident that the study of the inheritance of constitutional 

 predisposition to a disease must be almost impossible, where in- 

 fection is so general as in the case of tuberculosis. "We can only 

 hope to find instances of the inheritance of predisposition or re- 

 versely, of immunity to a bacterial disease in cases where we 

 are dealing with one, or with very few genetic factors, genes, 

 whose influence on the resistance happens to be very marked 

 indeed. 



Now, in principle, there are reasons to believe in the possi- 

 bility of an inheritance of immunity or predisposition for bac- 

 terial diseases. In the first place we have those instances, in 

 which closely related varieties or species differ in resistance to a 

 specific bacterial infection. A classical instance is that of the 

 Algerian sheep, which are constitutionally immune to anthrax. 



Another, similar instance was met by us in our work with rats. 

 "We found that there was a striking lack of uniformity in the 

 practical results of the use of a paratyphus culture as distributed 

 by the State Serum-institute of Holland for exterminating rats. 

 In some parts of Holland the broth-culture was highly effective 

 and very well spoken of, whereas it was almost wholly inef- 

 fective in other provinces. It appeared to us that this difference 

 might depend upon the species of rats against which the culture 

 was used. It was discovered by some joint work of the Koloniaal 



