198 LIFE OF ELIE METCHNIKOFF 



populations who feed almost exclusively on curded 

 milk live a very long time. In Bulgaria, for instance, 

 whole villages, thus fed, are known for the longevity 

 of their inhabitants. Starting from these considera- 

 tions, he made experiments upon himself and system- 

 atically introduced into his diet sour milk carefully 

 prepared with pure cultures of certain lactic bacilli. 

 His health was benefited by it, and his friends followed 

 his example. Certain doctors recommended sour 

 milk, the use of which gradually spread as a hygienic 

 food. MetchnikofE considered the result acquired as 

 a first step towards the artificial transformation of 

 the wild intestinal flora into a cultivated and useful 

 flora. 



Unfortunately, the study of the intestinal flora is 

 extremely complicated because of the innumerable 

 species of micro-organisms and the extreme difficulty 

 of disentangling the many influences which cross each 

 other. He therefore considered collective researches 

 as indispensable, the life and science of one man being 

 insufficient to solve so vast a problem. Up to a 

 certain point he succeeded in realising this scientific 

 collaboration within his own laboratory. 



