58 PHYSIOLOGY 



As they pass through, the pancreatic juice and the 

 secretion of the liver, the bile, which seems to aid the 

 digestion of fats, are poured in upon them. After about 

 two and a half hours the stomach is empty, and ready 

 for a period of rest. Digestion continues in the small 

 intestine and absorption occurs. The soluble substances 

 pass through the cell walls into the blood, which carries 

 them to all parts of the body. The residue of the food 

 passes on into the large intestine through a series of 

 contractions similar to those that take place in the 

 oesophagus. 



Absorption in the Intestine. — A special mechanism 

 fits the small intestine for absorption. Finger-like pro- 

 cesses called villi project from the inner wall (Fig. 38). 

 These contain a network of connective tissue, muscle 

 fibers, blood vessels and spaces connected with tube-like 

 channels called lacteals. Peptones and sugar pass into 

 the blood and are carried to the liver. Fats enter the 

 lacteals and reach the blood without being carried to the 

 liver. In the blood, peptones are changed back. to pro- 

 teids and the fat emulsion is changed back to fat. The 

 sugar remains sugar until it gets to the liver, when it is 

 changed to starch. 



The residue that passes into the large intestine is not 

 fit to nourish the body, but as long as it remains in the 

 intestine chemical action continues, and poisonous sub- 

 stances are formed which may be absorbed by the body 

 through the process of osmosis as readily as substances 

 which are nutritious. Therefore it is of importance 

 not to allow this residue to remain in the alimentary 

 canal until the system has been poisoned by it. 



