368 



THE AMERICAN NATURALIST [Vol. LTV 



INHERITED PREDISPOSITION FOR A BACTERIAL 

 DISEASE 



As soon as it can be demonstrated that in a process under in- 

 vestigation a given factor has a very marked influence, this 

 factor is more often than not looked upon as the sole cause of 

 what happens. It is indeed very difficult not to overemphasize 

 the importance of a new link in a chain of causes, which has been 

 hitherto overlooked, and which one is fortunate enough to dis- 

 cover. To give a few instances from a field familiar to us, we 

 can cite three factors in the evolution of species which have 

 each by one author been elevated to the rank of "the" cause of 

 species formation. Natural selection was the cause of evolution 

 in the eyes of Weismann, and every other factor was looked upon 

 as subordinate. In the same way "Wagner overemphasized the 

 importance of isolation, and de Vries would have us believe that 

 mutation was the main, if not the sole, cause of evolution. The 

 greatness of Charles Darwin lies in the fact, that he was not led 

 away from a consideration of all the possible factors by the temp- 

 tation to pad out the importance of any one link in the chain of 



In a few instances the discovery of a new and very important 

 factor in the causation of a process or set of phenomena sets all 

 the investigators working in the new field just opened up. And 

 often the attention is unduly taken away from other causes. In 

 pathology the discovery of the role which microorganisms play 

 in the causation of certain diseases has resulted in the almost 

 absolute neglect of the study of possible other factors in the 

 causation of these same diseases. 



In the illness of an individual, infection by a specific micro- 

 organism is a very important factor in certain cases. But it is 

 clear that, besides this infection, other factors influencing the 

 qualities of the subject can be of great importance. Very often 

 we find that, besides the presence of the specific organism, pre- 

 disposing factors play an important role, such as the simul- 

 taneous presence of another infection (tuberculosis after measles) 

 special conditions (diabetes, possibly beri-beri) ; causes lowering 

 the vitality (exhaustion, inanition). 



Besides factors of the environment, which in themselves are 

 not pathogenic factors, it is evident that factors given in the 

 composition of the individual, inherited factors, can cooperate in 



