THE GASTRO-INTESTINAL FLORA OF NORMAL INFANTS 583 



as it occurs in the intestinal contents, but which differs materially 

 from the latter both in its aerobiosis and in its inability to develop 

 bifid ends in artificial media. This organism, Bacillus acidophilus, 

 is more commonly found in the intestinal contents of artificially fed 

 babies than in nurslings, and it is more tolerant of organic acids than 

 Bacillus bifidus. It belongs to the group of Aciduric Bacteria. 1 



In addition to Bacillus bifidus 2 and Bacillus acidophilus, which 

 typically comprise a majority of the characteristic intestinal bacteria, 

 smaller numbers of Micrococcus ovalis, Bacillus coli, Bacillus lactis 

 aerogenes and other bacteria are found in the feces of nurslings. 



Escherich 3 has emphasized the very significant fact that putrefactive 

 (proteolytic) bacteria are uncommon in the dejecta of normal nurs- 

 lings; there is little or no evidence of the development of these 

 organisms in the intestinal tract during this stage. The putrefactive 

 bacteria, as a rule, do not develop in an acid medium in competition 

 with organisms like Bacillus bifidus and other acidogenic types which 

 dominate the alimentary canal of the normal nursling. 



Distribution of the Intestinal Flora of the Normal Nursling. The 

 principal portal of entry of the intestinal bacteria is the mouth. There 

 is no doubt that a great variety of organisms may from time to time 

 enter this atrium, including not only the ordinary organisms of the 

 nurslings' environment, but pathogenic bacteria as well. A majority 

 of these pass to the stomach, and they may pass to the intestinal 

 tract. The flora of the mouth and stomach are not well known, but 

 they appear to be of relatively slight importance as a rule. Those 

 adventitious organisms which pass from the stomach to the duodenum 

 rarely appear to gain a foothold there, or at lower levels of the 

 intestines. 



The duodenal flora, which in health is composed chiefly of coccal 

 forms of the Micrococcus ovalis type, is most numerous during those 

 periods when the food is passing through; during interdigestive periods 

 there appear to be relatively few bacteria at this level. From the 

 jejunum to the ileocecal valve, members of the Bacillus lactis aerogenes 

 group occur more commonly. Bacillus coli and other members of the 

 colon group are most numerous at the ileocecal valve and the cecum, 



1 Kendall, Jour. Med. Research, 1910, xxii, 153; Rahe, Jour. Inf. Dis., 1914, xv, 141. 



2 Madame Tsiklinsky (Ann. Inst. Past., 1903, xvii, 317) has been unable to demon- 

 strate B. bifidus in normal nurslings' feces as frequently as has been reported elsewhere; 

 the consensus of opinion appears to be, however, that bifidi are the most characteristic 

 bacilli of the normal nursling intestinal flora. 



3 Loc. cit. 



