CHAPTER XXX 



Intestinal flora Infantile cholera Typhoid fever Articles on popular 

 Science. 



WHEN he returned home, Metchnikoff immediately 

 resumed his work. He continued, with his colla- 

 borators, researches on the normal intestinal flora 

 and on the microbian poisons which provoke arterio- 

 sclerosis. 



They were able to ascertain that certain microbes 

 of the intestinal flora, such as the bacillus coli and 

 Welch's bacillus, produce poisons (phenol and indol) 

 which are reabsorbed by the normal intestinal walls 

 and which provoke arterio-sclerosis and other lesions 

 of the organs. A part of those poisons is eliminated 

 by the urine, and the quantity found therein allows 

 one to estimate the quantity contained in the 

 organism. An exclusively vegetarian or carnivorous 

 diet increases its production, while a mixed diet 

 reduces it. During the rest of his life MetchnikofE 

 made systematic and periodical analysis of his own 

 urine in correlation with his diet. 



From certain facts and certain experiments he con- 

 cluded that the reciprocal influence of microbes might 

 be utilised to attenuate or to eliminate the noxious 

 action of some of them. Thus, by cultivating the 

 lactic bacillus in the presence of those microbes which 

 produce poisons belonging to the aromatic group, the 



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