FERMENTED MILKS 



It has been shown in a previous chapter that under the influ- 

 ence of various fermentations, caused by groups of micro-organ- 

 isms, the normal condition of milk undergoes substantial altera- 

 tion. Fermented milks that have been used as food for ages are 

 the result of microbial activity and, according to the predominat- 

 ing kinds of micro-organisms, the product varies in character. 

 Fermented milks are used chiefly in Asia, the eastern parts of 

 Europe and in Egypt, but in western Europe and among uncivil- 

 ized tribes in Africa they are by no means unknown. 



The use of fermented milks has received material impetus of 

 late years through the publications of Metchnikoff, who asserted 

 and attempted to prove that auto-intoxication and premature 

 senility are due, in part at least, to poisonous substances produced 

 by putrefactive bacteria in the colon. This condition, Metch- 

 nikoff thought, could be combated by habitual consumption of 

 sour milk, the argument being that the acid produced by lactic 

 acid bacteria would prevent growth of putrefactive bacteria by 

 changing the chemical reaction of the digestive fluids in the ali- 

 mentary canal from alkaline to acid. Metchnikoff recommended 

 a fermented milk produced by a mixed culture, consisting of Ba- 

 cillus bulgaricus and Streptococcus lacticus, or, as Metchnikoff 

 calls this organism, the paralactic bacillus. 



In his book, "The Prolongation of Life," Metchnikoff develops 

 the theory that the cause of auto-intoxication and premature 

 senihty lies in the fact that food remnants accumulate in the large 

 intestine and are there decomposed by putrefactive bacteria. The 

 colon was evolved, so the author contends, to enable animals to 

 control defecation, and that this faculty was especially useful 

 when the animal was pursued by some enemy. This accumu- 

 lated food is subject to bacterial activity, and the cleavage prod- 

 ucts of protein invade the system from the colon and cause auto- 

 intoxication and premature senility. Metchnikoff illustrates his 

 hypothesis by the statement that birds have no colon and no 

 bladder, and are, therefore, compelled to defecate frequently. 

 The ostrich is an exception to this rule. It lives on the ground 

 and has more difficulty in escaping from an enemy than birds 

 that are able to fly, and, therefore, has developed a colon. Birds 

 are long lived, while terrestrial animals, as horses, cattle, sheep, etc., 

 are relatively short lived, a circumstance ascribed by Metchnikoff 

 to the fact that food remnants and waste products are held in the 



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