THE G ASTRO-INTESTINAL FLORA OF NORMAL INFANTS 585 



Bacillus acidophilus is relatively more numerous, as a rule, in the 

 artificially fed infant than in the nursling. Proteolytic bacteria of 

 several types are also of frequent occurrence, 1 but they are not com- 

 monly found in the dejecta of normal nurslings. These organisms are 

 frequently spore-forming bacilli, of which two principal groups are 

 recognized members of the aerobic group, of which Bacillus mesen- 

 tericus is a prominent type, and anaerobic bacteria; of the latter, 

 Bacillus aerbgenes capsulatus is most widely known; it frequently 

 occurs in small numbers in the feces of artificially fed infants. 2 The 

 reaction of normal feces of artificially fed babies is usually alkaline; 

 culturally and chemically, the evidence of intestinal proteolysis of 

 bacterial causation is more marked in these infants than in normal 

 nurslings. 



The general distribution of types of bacteria at the different levels 

 of the intestinal tract is similar to that observed in normal nurslings; 

 the principal differences are found in the cecum and large intestine, 

 where the obligately fermentative bacteria of the bifidus type are 

 replaced to a considerable degree by an extension of the habitat of 

 the colon bacillus, of Bacillus acidophilus, and the appearance of 

 moderate numbers of proteolytic bacteria, both aerobic and anaerobic; 

 many of the latter are sporogenic. 



The prevailing bacteria of the artificially fed infant may be changed 

 along fairly definite lines by varying the proportion of protein to 

 carbohydrate in the diet, and by substituting one carbohydrate for 

 another. Thus, a continued preponderance of protein leads to a partial 

 or even practically complete suppression of the activity of the 

 bifidus-acidophilus group, and a noteworthy increase in the activity 

 of proteolytic organisms; 3 of the latter, aerogenic bacteria of the 

 colon-proteus group and spore-forming bacteria of the mesentericus 

 group appear to be the more prominent. A relative increase in carbo- 

 hydrate leads to a diminution or suppression of proteolytic activity 

 in the intestinal tract, and an increase in the fermentative activities 

 of the intestinal organisms. 4 Those bacteria as Bacillus coli which 



1 Escherich, loc. cit. 



2 See Hibler (Untersuchungen liber die pathogenen Anaeroben, Jena, 1908), Jungano 

 and Distaso (Les Anaerobies, Paris, 1910) for description of various intestinal anaerobes. 

 Unfortunately, so little is definitely known about a majority of these organisms, cultur- 

 ally, chemically and numerically, that almost nothing can be said of their importance. 



3 Kendall, Jour. Biol. Chem., 1909, vi, 268; Herter and Kendall, ibid., 1910, vii, 203. 



4 Provided, of course, the digestion of the infant remains normal. It is obvious that 

 a disturbance of the digestive function of the alimentary canal may lead to new factors 

 which may play an important part in determining the prevalence of one or several types 

 of intestinal bacteria. 



