THE FECES 347 



A considerable number of species of bacteria exist in the body during life, 

 chiefly in connection with the mucous membranes, particularly of the digestive 

 tract. Many forms of bacteria have been isolated from the mouth, a few 

 varieties from the stomach, and a very large number from the intestines. It 

 is only in the last-named locality that their multiplication has much effect from 

 a physiological point of view. The normal (hydrochloric-acid) acidity of the 

 stomach usually destroys all the micro-organisms taken in with the food, but 

 when the amount of this acid is deficient (and sometimes even when it is nor- 

 mal) some of the spores may escape. On reaching the small intestine these 

 spores begin to develop in its alkaline medium, and may increase to such an 

 extent as to stop all intestinal digestion; the point where this occurs varies 

 from day to day. The large intestine always swarms with micro-organisms, 

 though they do not readily pass the ileo-cecal valve into the small intestine. 

 The bacteria found in the intestine are anaerobic, i.e., they do not develop in 

 the presence of free oxygen. 



The changes induced in the intestine by the activity of micro-organisms 

 are of two kinds, fermentation and putrefaction; the former of these results 

 in the breaking down of carbohydrate matter, and the latter in the disintegra- 

 tion of proteid matter. The process of fermentation is the less complex and 

 probably occurs normally in the small intestine to a certain extent. The lactic- 

 acid fermentation is the most important, though the butyric-acid fermentation 

 is next; under their influence the carbohydrates are broken down into lactic 

 and butyric acids, and perhaps into acetic acid also. Carbonic acid gas may 

 be formed at the same time and cause flatulence. Cellulose and other in- 

 soluble carbohydrates are decomposed, with the formation of marsh gas 

 and hydrogen, which escape by the rectum. 



In putrefaction the process is similar to that in tryptic digestion, the pro- 

 teids being broken down into peptones, leucin, tyrosin, and a long row of similar 

 substances. It also results in the production of various gases, such as carbon 

 dioxide, sulphureted hydrogen, ammonia, hydrogen and methane (marsh 

 gas), and of a high percentage of the volatile fatty acids, valerianic and butyric. 

 Of the aromatic substances the most important are indol and skatol, though 

 their toxicity has been greatly overestimated. Some undergo oxidation, indol 

 and skatol forming indoxyl and skatoxyl; they are usually carried off in the 

 feces, but when the bowel is obstructed they are absorbed and eventually 

 appear in the urine, indoxyl and skatoxyl forming respectively indoxyl- and 

 skatoxyl-sulphuric acids and their salts. Tyrosin is further broken down 

 into para-oxy-phenol-propionic acid, paracresol, and phenol; para-oxy-phenol- 

 acetic acid is also formed. Experiments have been performed to determine 

 whether or not the intestinal bacteria are neccessary to normal digestion. The 

 weight of evidence is in favor of the view that they are not. 



The Feces. The contents of the large intestine, as they proceed 

 toward the rectum, become more and more solid, lose more liquid and nutrient 



