VI. GENERAL DISCUSSION AND SUMMARY 



Under conditions of normal functioning the intestinal flora is funda- 

 mentally a physiological unit rather than a heterogeneous collection of 

 adventitious microorganisms, and bears a definite relation to the diet 

 of the host. 



The present study has shown that the types of bacteria developing 

 in the alimentary tract may be influenced in a noteworthy manner, not 

 only through special alterations in the chemical composition of the diet, 

 but also through the ingestion of living cultures of B. acidophilus with 

 or without accompanying carbohydrates. Only two of the carbo- 

 hydrates here employed, however, have the property of stimulating the 

 aciduric bacterial type, namely lactose and dextrin. 



Lactose and dextrin, when added in given amounts to the basal diet 

 (bread and meat) of the white rats or when taken by men in addition 

 to the usual daily diet, brought about a marked transformation of the 

 intestinal flora within four to six days, and stimulated the development 

 of B. acidophilus to such an extent that it largely or entirely dominated 

 the flora, eff'ecting an almost complete suppression of all other bacterial 

 types commonly found in the enteric tract. The simple flora persisted 

 as long as the feeding of these carbohydrates was continued. B. bifidus 

 occasionally increased in numbers under these dietary conditions, but 

 usually remained relatively obscure. It never became the dominant 

 type. 



These results are in harmony with those of certain other observers. 

 Barker (1914) and Torrey (1915) claimed to have secured favorable 

 results with the feeding of lactose and milk to typhoid fever patients. 

 Torrey demonstrated that the administration of a high carbohydrate 

 (lactose) diet tended to reduce the putrefying types of bacteria, and to 

 favor the growth of organisms of the B. acidophilus type. Our results 

 are in accord also with those of earlier investigations reported by Hull 

 and Rettger (1917) and the more recent announcements of Torrey 

 (1919), but they are diametrically opposed to those obtained by 

 Sisson (1917) in similar feeding experiments with puppies. Sisson 

 reported that a milk diet containing 10 to 15 per cent of lactose did 

 not cause an intestinal flora essentially difi'erent from that following a 

 diet of whole pasteurized milk. In fact, he failed to find any organisms 

 of the B. acidophilus type in any portion of the alimentary canal. 



In a short paper by Distaso and Schiller (1914) some feeding 



