96 ESSENTIALS OF CHEMICAL PHYSIOLOGY 



through which the absorbed subtances pass are living, and in virtue 

 of their vital activity not only select materials for absorption, but also 

 change those substances while in contact with them. These cells 

 are of two kinds : (1) the columnar epithelium that covers the 

 surface ; and (2) the lymph cells in the lymphoid tissue beneath. It 

 is now generally accepted that of the two the former, the columnar 

 epithelium, is the more important. When these cells are removed, or 

 rendered inactive by sodium fluoride, absorption practically ceases, 

 though the opportunities for simple nitration or diffusion would be by 

 such means increased. 



Absorption of Carbohydrates. Though the sugar formed from 

 starch by ptyalin and amylopsin is maltose, that found in the blood 

 is glucose. Under normal circumstances little if any is absorbed by 

 the lacteals. The glucose is formed from the maltose by the succus 

 entericus, and perhaps also by the vital action of the epithelial cells. 

 Cane sugar and milk sugar are also converted into glucose before 

 absorption. 



The carbohydrate food which enters the blood as glucose is taken 

 to the liver, and there stored up in the form of glycogen a reserve 

 store of carbohydrate material for the future needs of the body. 

 Glycogen, however, is found in animals which take no carbohydrate 

 food. It must then be formed by the protoplasmic activity of the 

 liver cells from their protein constituents. The carbohydrate store 

 leaves the liver in the blood of the hepatic vein as glucose (dextrose) 

 once more. 



The above is a brief statement of the glycogenic functions of the 

 liver as taught by Claude Bernard, and accepted by the majority of 

 physiologists. It has always been strongly contested by Pavy, who 

 holds that the glycogen formed in the liver from the sugar of the 

 portal blood is never during life reconverted into sugar, but is used 

 in the formation of other substances like fat and protein ; in support 

 of this he has shown that proteins contain a carbohydrate radical. 

 He denies that the post-mortem formation of sugar from glycogen 

 that occurs in an excised liver is a true picture of what occurs during 

 life. 



Absorption of Proteins, It is possible that under abnormal con- 

 ditions a certain amount of soluble protein is absorbed unchanged. 

 Thus, after eating a large number of eggs, egg-albumin has been 

 stated to be discoverable in the urine. Patients fed per rectum derive 

 nourishment from protein food, although proteolytic ferments are not 

 present in this part of the intestine. 



Under normal conditions, however, the food-proteins are broken 



