DIGESTION AND ABSORPTION IN THE INTESTINES. 717 



also for parts of the large intestine. It is, moreover, borne out by 

 the medical practice of giving enemata into the rectum when the 

 conditions are such that the patient can not be fed in the normal 

 way. That absorption and utilization of the proteid take place 

 under such conditions is shown not only by the improved nutritive 

 condition of the individual, but also by the increased output of 

 nitrogen in the urine. This phenomenon occurs in parts of the 

 intestinal canal in which normally no proteolytic enzymes occur, so 

 that the whole process must be referred to an activity of the cells 

 composing the walls of the intestine. There seems at present little 

 grounds for a satisfactory explanation of the absorption of proteids, 

 with or without digestion, by a direct application of the known 

 laws of osmosis, diffusion, and imbibition. Examination of the 

 contents of the small intestine at its junction with the large shows 

 that under normal conditions most of the proteid has been ab- 

 sorbed before reaching this point. The process is continued in the 

 large intestine, modified somewhat by bacterial action, and the 

 amount that finally escapes absorption and appears in the feces 

 varies, in perfectly normal individuals, with the character of the 

 proteid eaten. According to Munk,* the easily digestible animal 

 foods such as milk, eggs, and meat are absorbed to the extent of 

 97 to 99 per cent., while with vegetable foods the utilization is less 

 complete; from 17 to 30 per cent, of the proteid may be lost in the 

 feces if the vegetable food is in such form as not to be attacked readily 

 by the digestive secretions. 



Digestion and Absorption in the Large Intestine. Observa- 

 tions upon the secretions of the large intestine have been made upon 

 human beings in cases of anus prseternaturalis, in which the lower 

 portion of the intestine was practically isolated, and also upon 

 lower animals, in which an artificial anus was established at the 

 end of the small intestine. These observations all indicate that 

 the secretion of the large intestine, while it contains much mucus 

 and shows an alkaline reaction, is not characterized by the presence 

 of distinctive enzymes. When the contents of the small intestine 

 pass the valve they still contain a certain amount of unabsorbed 

 food material. As was stated in the chapter on the movements of the 

 intestine, this material remains a long time in the large intestine, and 

 since it contains the digestive enzymes received in the duodenum the 

 digestive and absorptive processes no doubt continue as in the small 

 intestine. This general fact is well illustrated in experiments made 

 upon dogs most of whose small intestine (70 to 83 per cent.) had been 

 removed.f These animals could digest and absorb well, and formed 



* See Munk, " Ergebnisse der Physiologic, " vol. i, part i, 1902, article, 

 " Resorption," for literature and discussion. 



t Erlanger and Hewlett, "American Journal of Physiology," 6, 1, 1902. 



