128 THE PHYSIOLOGY OF DIGESTION AND ABSORPTION 



continual absorption of the fluid portions, until the pultaceous 

 mass received by the cecum becomes almost solid in the sigmoid. 

 The degree of consistence may be said to be greater the longer 

 the sojourn in the large intestine. The proteids and carbohy- 

 drates which have escaped absorption in the small intestine are 

 disposed of here, partly by bacterial decomposition, and do not 

 appear as such in the feces. The absorption of easily digestible 

 substances in solutions, such as eggs, etc., from the lower bowel, 

 although there is no digestive enzyme there, is a matter of com- 

 mon observation, but one which lacks explanation. 



Forms in Which the Different Classes are Absorbed, i. 

 Water and Salts. Of course, water is absorbed in connection 

 with all the foods as a vehicle for them, but water and salts as 

 such have been shown to be absorbed sparingly in the stomach. 

 They are soon conveyed to the small intestine, where their rapid 

 disappearance ensues. However, they may be absorbed any- 

 where in the alimentary canal. The loss of the water from the 

 alimentary mass in the upper small intestine is compensated for 

 by the secretions, so that the fluidity of the contents is not mate- 

 rially affected until the colon is reached. Here absorption of 

 water is active, and the mass becomes more and more solid as the 

 rectum is approached. 



2. Proteids. It is agreed that the first object of proteid diges- 

 tion is to render the nitrogenous foods more diffusible. It is 

 also agreed that the end products of such digestion, so far as 

 alimentary absorption is concerned, are proteoses and peptones; 

 and the natural conclusion, supported by experimental evidence, 

 is that these represent the forms in which the proteids are ab- 

 sorbed. True, leucin, tyrosin, etc., further end products of 

 proteolysis, are formed, but these cannot be absorbed. The 

 opinion that proteoses and peptones are the absorbable forms of 

 proteids is correct, for by far the largest part of these foods are 

 absorbed in this shape. It is supposed also that syntonin at 

 least can itself be sparingly absorbed from the alimentary canal, 



