cu. xxxnr.] THE ABSORPTION OF FOOD. 



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, aided by the action of the 

 epithelial cells through which it passes. 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 who take no 

 carbohydrate food. It must, then, be formed by the proto- 

 plasmic activity of the liver cells from their proteid constituents. 

 The glycogenic function of the liver is discussed in the chapter 

 preceding this. Glucose is the only sugar from which the liver 

 is capable of forming glycogen. If other carbohydrates like cane 

 sugar or lactose are injected into the blood-stream direct, they are 

 unaltered by the liver, and finally leave the body by the urine. 



Absorption of Proteids. A certain amount of soluble 

 proteid is absorbed unchanged. Thus, after taking a large 

 number of eggs, egg albumin is found in the urine. Patients 

 fed per rectum derive nourishment from proteid food, though 

 proteolytic ferments are not present in this part of the intestine. 



Most proteid, however, is normally absorbed as peptone and 

 proteose (albumose). Peptones and proteoses are absent from 

 the blood under all circumstances, even from the portal blood 

 during the most active digestion. In other words during absorp- 

 tion the epithelial cells change the products of proteolysis 

 (peptones and proteoses) back once more into native proteids 

 (albumin and globulin). 



The greater part of the proteid absorbed passes into the blood ; 

 a little into the lymph vessels also ; but this undergoes the same 

 change. 



When peptone (using the- word to include the proteoses also) 

 is injected into the blood-stream, poisonous effects are produced, 

 the coagulability of the blood is lessened, the blood pressure falls, 

 secretion ceases, and in the dog 0*3 gramme of " peptone " per 

 kilogramme of body weight is sufficient to kill the animal. 



The epithelial cells of the alimentary canal thus protect us 

 from those poisonous effects by converting the harmful peptone 

 into the useful albumin. 



Absorption of Fats. The fats undergo in the intestine two 

 changes : one a physical change (emulsification), the other a 

 chemical change (saponification). The lymphatic vessels are the 

 great channels for fat absorption, and their name lacteals, is 



K.P. L L 



