MICROORGANISMS OF THE DIGESTIVE TRACT 597 



may be altered by changing the character of the diet, a fact of impor- 

 tance in the treatment of intestinal infections. 



In the caecum there is a sudden enlargement of the lumen of the 

 intestinal canal and a consequent retardation of the movement of 

 the intestinal contents. The blind pouch also favors stagnation. In 

 this region the whole intestinal contents usually acquire a chemical 

 reaction neutral or alkaline to litmus. All these factors favor the 

 enormous multiplication of bacteria. Indeed, the caecum and the 

 remaining large intestine constitute the great bacterial incubator of 

 the healthy body. Here B. coli multiplies enormously; the strict 

 anaerobes, Bad. Welchii and B. edematis flourish under most favorable 

 conditions. Various streptococci, staphylococci and spirochetes multi- 

 ply either in the food residues or in the intestinal secretions. An 

 easily digested mixed diet favors the facultative anaerobes, while excess- 

 ive feeding of starchy foods and of meat leads to an overgrowth of the 

 strict anaerobes, especially those of the Bact. Welchii group. Many of 

 these bacteria will then be found to stain blue with iodine, giving the 

 s6-called granulose reaction. A milk diet, especially if limited in 

 amount and well digested by the individual, favors the micro-aerophilic 

 B. bifidus of Tissier, the organism which is dominant in the faeces of the 

 healthy breast-fed infant and occasionally very abundant even in 

 adults. 



In the lower portions of the large intestine, as a result of progressive 

 absorption from the contents of the bowel, there is a concentration 

 and overcrowding of the bacteria which have developed at higher levels. 

 The vast majority of them die and these dead cells, together with the 

 still abundant living microorganisms, make up about a third of the 

 substance of the faeces. The faeces are composed of rejected food 

 residues, residues of intestinal secretions, of bile and pancreatic juice 

 and abundant microorganisms, some of the latter still actively multi- 

 plying, but the majority of them dead and in various stages of 

 disintegration. 



THE MICROORGANISMS OF THE F^CES. The microorganisms of the 

 faeces represent the end result of the progressive multiplication or dis- 

 integration, or both, of the organisms originally present in the food 

 together with all those added at various regions of the alimentary canal. 

 The microbic flora of the large intestine is, however, most prominent 

 in the faeces. The total quantity and the proportions of the various 



