PHYSIOLOGY OF DIGESTION 43 



(a) Amylopsin, which changfes the insoluble starch into soluble 

 sugar. 



(b) Trypsin, which converts insoluble protein into soluble 

 peptone. 



(c) Steapsin, which emulsifies the fats and oils in the food, 

 and renders them more easy of absorption into the circulation. 



7. Absorption. — This is the step by which the nutrient ma- 

 terials of the food, in liquid form, are taken from the alimentary 

 canal into the circulation to be carried by the blood to all parts 

 of the body to nourish the different tissues. And no food is 

 capable of being absorbed until it has first been rendered soluble 

 by the action of the different ferments. 



Intestinal absorption takes place through the villi of the small 

 intestines into the lacteals — small beginnings of the lymphatic 

 system distributed to the small intestine — and through the blood- 

 vessels into the venous system. The nutrients absorbed by the 

 bloodvessels pass into the portal vein and are conveyed by this 

 vein to the liver before entering into the circulation. Hence the 

 nutrients either pass through tlie lymphatic glands to the blood 

 or else are conveyed to the liver for further elaboration before 

 entering the circulation. 



Fats. — The fats are generally emulsified before being absorbed. 

 The lacteals are considered as absorbing all the fats. 



Sugar formed in the bowel reaches the circulation through the 

 portal vein and liver. Some of it in the horse perhaps finds its 

 way to the lacteals. We will learn in the next section that the 

 excess of sugar in the blood is; taken up by the liver and con- 

 verted into starch (glycogen) and doled out in the form of sugar 

 to the blood as required. Mineral salts in solution enter the 

 blood as do the sugars. 



Froteids. — As already stated the proteids are converted into 

 peptones before being absorbed. It is said that the peptones are 

 absorbed by the bloodvessels of the villi, and conveyed by the, 

 portal vein to the liver. 



8. Circulation. — This step is accomplished by the blood in the 

 arteries carrying the nutritive materials, absorbed from the food, 

 to all parts of the body. 



