PROCESSES IN THE LARGE INTESTINE. 335 



The remarkable fact should yet be mentioned here that the putrefactive 

 processes, after the development of phenol, indol, and skatol, and also of cresol, 

 phenyl-propionic and phenylacetic acids, are again inhibited, and after a certain 

 concentration in their production cease completely. Thus, the putrefactive pro- 

 cess itself generates antiseptic substances even to the point of causing the death 

 of the micro-organisms; for, as with highly organized beings, the excremen- 

 titious products of the bacteria themselves are poisons for them. It is, there- 

 fore, to be inferred that, in the intestinal canal also, the formation of the sub- 

 stances mentioned in turn inhibits the putrefactive decompositions to some ex- 

 tent. Ptomains are not formed normally in the intestines. 



The reaction of the contents of the small intestine is alkaline, due 

 principally to carbonates, and in less degree to phosphates. The con- 

 tents are, however, rich in carbon dioxid, the presence of which causes, 

 on one hand, the acid reaction of the indicators reacting to carbon 

 dioxid, while, on the other hand, it ensures the maximum efficiency on 

 the part of the ferments in the intestine. In the large intestine' the 

 reaction is generally acid, in consequence of the acid fermentation and 

 decomposition of the ingesta and the feces. 



PROCESSES IN THE LARGE INTESTINE. FORMATION OF THE 



FECES. 



Within the large intestine the putrefactive and fermentative decom- 

 positions of the ingesta greatly exceed the fermentative or true digestive 

 transformations, as only small amounts of the ferments of the intestinal 

 juice are found in it. In addition, the absorptive activity of the walls 

 of the large intestine is greater than the secretory activity, whence the 

 consistency of the contents, which at the commencement of the large 

 intestine are still semi-liquid, but become more consistent in the further 

 course of the intestine. The absorption includes not only the water and 

 the products of digestion in solution, but also, under certain circum- 

 stances, even unchanged fluid proteids. Also toxic substances are de- 

 cidedly more readily absorbed here than from the stomach. The feces 

 begin to be formed only in the lower portion of the large intestine. The 

 cecum in some animals, as, for example, the rabbit, is of considerable 

 size ; fermentative decompositions appear to take place in it with great 

 activity, with the development of an acid reaction. In human beings 

 the cecum is principally an organ of absorption, as the abundance of 

 lymphatic follicles indicates. From the lower portion of the small in- 

 testine and from the cecum onward, the ingesta acquire the fecal odor. 



Observations on Thiry's intestinal fistulae permit the conclusion that 

 a considerable portion of the feces is derived from the secretion of the 

 mucous membrane and from epithelial desquamation. 



The amount of feces evacuated equals, on an average, 170 grams in 

 twenty-four hours (from 60 to 250 grams), although, when large amounts 

 of food, especially if difficult of digestion, are taken, even more than 500 

 grams may be discharged. After a diet of animal food the amounts of 

 feces and of solid residue therein are less than after a vegetable diet. The 

 consistent feces are broken up by the development of gas, and there- 

 fore float on water. 



The consistency of the feces depends on the amount of water con- 

 tained in them, which usually reaches 75 per cent. A pure meat- 

 diet causes rather dry feces; food rich in sugar, rather watery feces; 

 while the amount of fluid ingested is without influence. The more 



