50 INFECTIONS OF THE DIGESTIVE TRACT 



derived from the skin and nipple Staphylococcus 

 pyogenes aureus, bacilli of the B. coli group and B. lactis 

 aerogenes. In the stomach the number of bacteria is 

 also small, and the bacterioscopic picture shows usually 

 a few positive or negative diplococci or streptococci or 

 negative cocco-bacilli or positive or negative bacilli, 

 suggesting the B. coli and B. lactis aerogenes group. The 

 duodenum and jejunum generally contain remarkably 

 few microorganisms, owing mainly to the rapidity with 

 which the food passes through this region. When food 

 in the jejunum is present in larger amount than is usual, 

 the numbers of bacteria are correspondingly increased, 

 but it is the rule that the greater part of the small intes- 

 tine is almost free from bacteria and that they do not 

 become really numerous until the level of the lower ileum 

 is reached. Here there is almost regularly an abrupt 

 increase in the bacterial flora. In the csecum (and like- 

 wise in the vermiform appendix) the bacterial increase 

 is enormous. The normal bacteria of the greater por- 

 tion of the small intestine are Gram-negative, short bacilli 

 of the coli and lactis aerogenes variety, mixed sometimes 

 with a few positive and negative coccal forms. In the 

 lower ileum the Gram-negative forms become mixed with 

 those of the bifidus type, especially the punctate bacilli. 

 The transition from lower ileum to caecum marks, as a 

 rule, a striking change in the proportions of coli and 

 bifidus types, since the former lose their dominant nu- 

 merical position. This ascendency of the bifidus type is 

 so great in the transverse and descending colon that all 

 other bacteria in these regions are numerically incon- 



