THE GASTRO-INTESTINAL FLORA OF NORMAL INFANTS 591 



an excess of protein; if maltose or dextrose is substituted for lactose 

 under the same conditions, Bacillus acidophilus is very frequently 

 the more prominent. In like manner, the nature of the protein 

 influences the types of proteolytic bacteria to a very marked degree; 

 in general, animal proteins other than casein appear to encourage a 

 somewhat more active proteolytic flora than vegetable proteins. These 

 observations are in harmony, in essential features at least, with those 

 made under like conditions in man. A monotonous diet in which lac- 

 tose and protein are fed in proportions and amounts similar to breast 

 milk leads to the gradual development of an intestinal flora in experi- 

 mental animals closely simulating that of nurslings. A preponderance 

 of protein, on the other hand, encourages the development of bacteria 

 which are more proteolytic in nature. 



It is a striking fact that the above alternation in intestinal bacteria 

 following changes along definite lines in the diet is elicited only when 

 the feeding is maintained for several days; rapid alternations between 

 a purely protein diet and a diet rich in sugar (as cow's milk diluted 

 with an equal volume of 4 per cent, lactose solution) do not ordinarily 

 lead to such noteworthy changes in the types of bacteria excreted in 

 the feces. 1 The general trend of such rapid alternations between a 

 protein regimen and one in which sugars predominate (starches do 

 not necessarily react in this manner) is to establish a flora which is 

 relatively heterogeneous, in which there is neither a decided predom- 

 inance of obligately carbohydrophilic bacteria, as B. bifidus or acido- 

 philus, nor of obligately proteolytic bacteria. 



A most striking and important influence of diet upon bacterial 

 activity in the intestinal tract does not manifest itself in a study con- 

 fined exclusively to the changes in bacterial types of the intestinal 

 flora. The monotony of the typical nursling flora depends in a large 

 measure on the continual presence of lactose (a sugar not fermented 

 by a majority of bacteria) throughout the intestinal tract. A sub- 

 stitution of other sugars as dextrose, saccharose or maltose leads 

 to a replacement of Bacillus bifidus by other more or less obligately 

 fermentative organisms, provided an excess of the respective carbo- 

 hydrate be maintained, but the same monotony of types is observed. 



The proportion of carbohydrate to protein in the diet of normal 

 adults is far less than in nurslings and, furthermore, a considerable 

 proportion of the carbohydrate is in the form of starches which, as 



1 This probably explains some of the irregularities experienced during brief feeding 

 experiments. 



