34 FEEDS AND FEEDING 



with the veins. If one extends his arms in front of him with his finger tips 

 touching, his body will represent the heart, while one arm will represent 

 an artery carrying blood from the heart, and the other a vein conveying 

 blood to the heart. The touching fingers will correspond to the capillaries 

 connecting the arteries with the veins, and the space all about the fingers 

 will represent the surrounding body tissues. In general, neither the 

 veins nor the arteries allow any substance within them to escape thru 

 their walls proper. It is thru the capillaries that the nutritive matter 

 carried by the blood finds its way into the body tissues for their nourish- 

 ment, and thru the capillaries and the lymphatics, in turn, the waste of 

 the body drains back into the blood circulation. 



The digested nutrients are absorbed into the circulation of the body 

 chiefly by the mucous membrane of the small intestine. In order to pro- 

 vide a larger surface so that the nutrients may be more readily and com- 

 pletely absorbed, this mucous membrane has innumerable cone-like pro- 

 jections, called mill. These villi, which give the mucous membrane a 

 velvety appearance, project toward the center of the intestinal tube 

 and thus come into intimate contact with the fluid contents. Within 

 each villus are lacteals, or drainage tubes of the lymphatic system, and 

 capillaries of the blood system. The veins from the intestine unite 

 and form the portal vein, which carries the absorbed nutrients to the 

 liver and then on to the heart. 



59. Absorption of fat. As has been previously explained, thru the 

 action of the lipase in the pancreatic juice and the alkalies in the bile, 

 practically all the fat in the food is changed into soaps and glycerin. 

 The bile aids in dissolving these soaps, so they are more readily absorbed 

 by the villi of the small intestine. In the villi the soaps and the glycerin 

 are reconverted back into fat, which then enters the lacteals in the villi, 

 forming with the lymph a milky substance called chyle. This is carried 

 in the lymphatics and poured into a vein near the shoulder, thus enter- 

 ing the blood circulation. 



60. Absorption of carbohydrates; formation of glycogen.- Thru the 

 action of the ptyalin of the saliva, the amylase of the pancreatic 

 juice, and the invertases of the intestinal juice, a very complete diges- 

 tion of the starch and the compound sugars in the food occurs, in which 

 they are all converted to glucose or other simple sugars. These are 

 absorbed chiefly by the villi of the small intestine, passing into the capil- 

 laries and then entering the veins. When the sugars reach the liver, 

 they are for the most part withdrawn from the blood and temporarily 

 stored in this organ as glycogen, a carbohydrate which is closely related 

 to starch and, having the same percentage composition, is sometimes 

 called animal starch. Normally from 1.5 to 4.0 per ct. of the weight 

 of the liver consists of glycogen. The glycogen stored in the liver is 

 gradually changed back into glucose, and then doled out to the system 

 as required, the amount of glucose in the blood being kept at about 1 

 part in 1,000. The property of converting glucose into glycogen is not 



