GENERAL DISCUSSION AND SUMMARY 121 



types ordinarily present in the alimentary canal. It is of interest, too, 

 to know that two cubic centimeters and 300 cubic centimeters respec- 

 tively of the suspension, when fed daily to rats and to man, are suffi- 

 cient to effect the transformation, and the maintenance of the simple 

 flora. 



Since the bacteria within the digestive tract procure their pabulum 

 directly or indirectly from the diet consumed by the host, it is logical 

 to assume that there is a definite relation between the chemical nature of 

 the ingested food and the metabolic activities of the intestinal organisms. 

 Many investigators have noted that marked changes in the intestinal 

 flora follow sharp alterations in the diet ; namely, that a proteolytic or 

 putrefactive flora results from high protein feeding, and that a carbo- 

 hydrolytic or fermentative flora develops when the protein intake is low 

 and the diet consists largely of carbohydrates. However, the ordinary 

 high-calory diets accomplish reformation only, and not a simplification 

 of the intestinal flora, that is, a change from the putrefactive to the 

 fermentative state of metabolism. As soon as the proper carbohydrate- 

 protein ratio is disturbed the reformed intestinal tenants begin to sin 

 and putrefactive metabolism again holds sway. 



The harmful effects caused by, or associated with, pathogenic organ- 

 isms of exogenous origin, such as B. typhosus, B. dysenteriae, Ms. 

 cholerae, need no further comment. But it should be a matter of much 

 concern that the so-called "normal" organisms of the intestinal canal 

 may occasionally bring about decidedly abnormal conditions. Booker 

 (1897) claimed that Proteus vulgaris and certain streptococci may 

 elicit diarrheas in infancy. Bertrand (1914) found Proteus vulgaris 

 in each of his fifty-five patients suffering from diarrhea. Schumburg 

 (1902) reported the same organism as the cause of poisoning following 

 the consumption of sausages. Klein (1896, 1898) concluded that 

 B. welchii is an important factor in the causation of infantile diarrhea, 

 and Tissier (1905) described cases of acute diarrheas caused by this 

 organism. More recently Kendall and his associates (1911, 1913) and 

 Smith (1913) gave expression to similar observations and views. 



Senator (1868) declared that the decomposition of proteins within 

 the intestinal canal under ordinary conditions results in the formation 

 of substances toxic to the host. Bouchard (1884) elaborated the 

 theory of auto-intoxication. Combe (1907) stated that food too rich 

 in nitrogen will cause intestinal auto-intoxication. Metchnikoff pub- 

 lished his views on the same subject, calling attention to a definite 

 alleged relation between premature senility and intestinal putrefaction. 

 He claimed that the proteolytic intestinal organisms are constantly 

 producing substances which are absorbed by the host and which act 

 as accumulative poisons. Metchnikoff proposed to fight these proteolytic 

 bacteria on their own battlefield by the introduction of an antagonistic 

 microbic army, the lactic acid bacilli, and thus ushered in a new and 



