CHAPTER III 



THE NATURE OF THE ADAPTATIVE PROCESS IN THE BACTERIA 



In fact, studying the bacteria, two apparently opposite and 

 contradictory facts are to be made out : on the one hand they 

 are extraordinarily conservative to the extent that, given the 

 same environment, the same food-stufis, habit of lif e, temperature 

 conditions, etc., they manifest the same characters, and even, 

 within certain limits when the environment is altered, they 

 retain their original characters with a certain obstinacy. Typhoid 

 bacilli from cases of Enteric show scarce recognizable differences, 1 

 whether occurring in England, Australia, North America, or 

 Japan. And on the other hand, alter their environment beyond 

 certain limits — their food-stuffs, temperature of growth, etc. — 

 and their characters are liable to alter. Grow the diphtheria 

 bacillus, for example, in peptone broth, in milk, or upon peptone 

 broth agar, and this at the same temperature, and at the end 

 of twenty-four hours the differences are recognizable under 

 the microscope. Nothing, in fact, is more easy to demonstrate 

 than this capacity on the part of bacteria as a class to vary 

 according to alteration in environment. 



Fluctuations, Mutations, and Modifications 



Winslow divides these variations exhibited by bacteria into 

 three orders, (1) fluctuations, (2) mutations, and (3) impressed 

 variations. Some term these last, modifications. Personally, 



1 Several years ago Ehrlioh pointed out to me the difference between the 

 results of his diazo reaction in our Montreal cases of typhoid as compared with 

 his results in Germany, and suggested that we might be dealing with distinct 

 strains of the B. typhosus. Sir William Osier tells me that similarly he is 

 impressed by the difference in the bodily reactions to tertian malaria as acquired 

 in the Salonica area, and as he was familiar with it in Maryland. 



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