FERMENTED MILKS 393 



large intestine for a considerable length of time, sometimes for 

 several days, and are then subject to putrefactive decomposition 

 by bacteria. According to the author's theory, the protein cleav- 

 age products enter the circulation and tend to abbreviate the 

 lives of these animals. 



Herter also believes that premature senility is due, in part at 

 least, to putrefactive products of anaerobes. Bacillus welchii is 

 considered by this author as one of the chief offenders. He states 

 further that the character of the food influences the intestinal 

 flora both numerically and in kind. In the upper portion of the 

 intestinal canal of infants fed on human milk the Bacillus bifidus 

 of Tissier is prominent, and, as this organism which belongs to the 

 group of lactobacilli produces a relatively large amount of acid, 

 other bacteria are largely suppressed. The intestinal flora of 

 infants fed on cow's milk is decisively different from that of those 

 fed on human milk, as different types of bacteria, including some 

 anaerobes, are present in considerable numbers. 



In the stomachs of adults relatively few bacteria exist because 

 of the germicidal effect of the hydrochloric acid in the gastric 

 juice. But farther down in the digestive tract the number of 

 bacteria increases, and in the colon they are present in enormous 

 numbers, the number being so great that, according to some 

 authors, 33 to 45 per cent, of the fecal discharges consist of living 

 and dead bacteria. 



The bacterial flora in the intestines of birds is considerably 

 smaller than that of terrestrial animals, and it is to this condition 

 that Metchnikoff ascribes the greater longevity of birds as com- 

 pared with terrestrial animals. In other words, the bacterial 

 flora in the intestines of terrestrial animals produces powerful 

 decomposition products from the food remaining in the colon. 

 Birds, having no colon, discharge waste products frequently, and 

 consequently have a small bacterial flora. The formation of 

 protein decomposition products in birds is also relatively small 

 because of frequent defecation and consequent lack of food for 

 the bacteria. 



Conditions obtaining in the colon are eminently suitable for 

 the growth of putrefactive bacteria, especially anaerobes. The 

 oxygen which reaches the stomach with food is gradually absorbed 

 not only by living organisms but also by food remnants, especially 

 meat. Furthermore, the reaction of the contents of the lower 

 intestine is alkaline and part of the food may not be properly 

 digested, due, in a measure, to imperfect mastication. Therefore 

 food, absence of oxygen, and suitable temperature combine to 

 render the colon a favorable place for the growth of anaerobes. 



Protein cleavage products, chiefly oxyacids, indol and phenol 



