INFECTIONS OF THE DIGESTIVE TRACT 39 



lus (Moro). These bacilli are not surely distinguishable 

 from B. bifidus in the Gram-stained field. Although 

 B. bifidus thus dominates the typical field, other Gram- 

 positive bacteria can always be found. Of these the 

 most important (though very few in number) are large, 

 plump bacilli, occurring usually singly, but sometimes 

 in pairs. This is the B. aerogenes capsulatus (B. Welchii 

 or gas-phlegmon bacillus of Fraenkel). As will be seen 

 later, it may play an important part in the pathology 

 of the digestive tract. Another Gram-positive organism 

 which is regularly present in small numbers in the field 

 is a diplococcus which frequently grows in chains. This 

 coccus is commonly associated with a similar organism 

 which is Gram-negative. The chief remaining Gram- 

 negative bacteria are small coccal or coccoid forms and 

 shorter and longer bacilli which by cultural methods 

 can be shown to have the biological characters of the 

 B. lactis aerogenes group and the B. coli communis 

 group. 



Thus by means of the Gram method of staining one 

 finds that the typical field from the nursling's stool is 

 predominantly Gram-positive and consists very largely 

 of slender bacilli which but for their retention of the dye 

 might be regarded as colon bacilli, and were indeed so 

 regarded by Escherich, who in his original studies em- 

 ployed gentian violet as the sole staining agent. The 

 fact that the bacterial fields from the nursling are Gram- 

 positive is now familiar, but it came to those who first 

 observed it as a distinct surprise. It was known that 

 the B. coli group of bacteria are Gram-negative, and as 



