CHAPTER XXXI 



A bacteriological expedition to the Kalmuk steppes, 1911. 



DURING his preceding journeys in the Kalmuk steppes, 

 Metchnikoff had often heard it said that tuberculosis 

 was almost unknown there, but that the Kalmuks 

 took it very easily when brought into contact with 

 foreigners. As all means of combating this disease 

 had hitherto given very unsatisfactory results, Metch- 

 nikoff thought that researches should be started along 

 a new path. He had long thought that observations 

 on the extreme liability of Kalmuks to tuberculosis 

 might perhaps provide some new data. But the 

 study of the question necessitated a very distant 

 jpurney which he now at last had the opportunity of 

 realising. 



According to Metchnikoff's hypothesis, a natural 

 vaccination takes place among us against tuberculosis 

 which would explain the resistance of the majority 

 of human beings in spite of the enormous diffusion 

 of the disease. He concluded that some attenuated 

 breeds of microbes become introduced into our 

 organism during our childhood, thus vaccinating us 

 against the virulent tuberculous bacillus. This sup- 

 position seemed to him plausible, for he had long 

 ago found that some micro-organisms (Cienkovsky's 

 bacillus, the cholera bacillus, etc.) become modified 

 in different environment and conditions, both in form 

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