LIFE OF ELIE METCHNIKOFF 197 



and lie enquired whether the intestine sheltered 

 putrefying microbes. This question had not yet been 

 solved ; certain bacteriologists thought that little or 

 no putrefaction exists in a normal intestine. Metch- 

 nikoff ascertained through systematic researches that 

 the intestinal flora includes several kinds of putrefying 

 microbes which secrete highly toxic products. 



With his pupils and collaborators, MM. Berthelot 

 and Wollman, he carried out a series of experiments 

 which established the fact that this intoxication is 

 due to poisons of the aromatic group, such as phenols 

 and indols. With these substances, they succeeded 

 in artificially provoking arterio-sclerosis in the organs 

 of animals, and also other modifications similar to 

 those which are observed in senility. Having proved 

 that putrefying microbes provoke the intoxication 

 of the tissues, Metchnikoff set to work to find a 

 means of struggling against those microbes. 



It was known that they could only live in an 

 alkaline medium which is precisely that of the intes- 

 tinal juices. Metchnikoff thought that if means were 

 found to render the intestinal contents acid, without 

 harm being done to the organism, the putrefying 

 microbes might thus be destroyed. It had been 

 known for a long time that sour milk does not 

 suffer putrefaction, that being prevented by the acid 

 fermentation. The lactic microbes of this fermenta- 

 tion must therefore be antagonistic to the putrefy- 

 ing microbes. He drew a conclusion in favour of 

 the utility of sour milk, containing acid-producing 

 microbes ; once introduced into the intestine, these 

 should prevent the breeding of the noxious microbes 

 which require an alkaline medium. 



His hypothesis seemed confirmed by the fact that 



