314 THE ANIMALS AND MAN 



Water and salts pass into the blood mainly in the small 

 and large intestine. 



Alcohol is absorbed very quickly through the walls of the 

 stomach. Its quick action upon the body is probably due 

 to this fact. 



Action of the liver upon nutrients.-^Absorbed food is 

 carried immediately by a large blood vessel (the portal vein) 

 to the liver. Here it undergoes further changes before it is 

 distributed to the cells of the body. Here glycogen or liver 

 starch is formed of any normal excess of sugar in the blood and 

 held as a reserve supply. Here, also, any poisonous com- 

 pounds, that may have been absorbed with the food and 

 that might injure the tissues, are removed. 



The large intestine. — During its passage through the 

 small intestine most of the digested food is absorbed, as we 

 have learned. The undigested parts of the food, together 

 with such poisons as have been collected by the liver, pass into 

 the large intestine and out of the body through the rectum, 

 by peristalsis. Constipation is the clogging of the rectum 

 or large intestine. Constipation is dangerous because the 

 poisons from the liver become reabsorbed. This results 

 in biliousness, headache and often very serious troubles. 



Hygiene of eating and digestion. — The body requires 

 that some proteid, carbohydrate and fat and water shall 

 be absorbed each day. The digestive system is regulated 

 to care for a certain amount only. If too much is demanded 

 of the alimentary canal, digestion is impaired and dyspepsia 

 results. Digestion is a "chain of results;" first the cooking, 

 then the masticating, and finally solution in the digestive 

 juices. All this takes care and time. A poorly cooked 

 meal or a hurried meal means a partially digested meal. 

 Lack of the right kind of food and of exercise engender con- 

 stipation. Indigestion and constipation are the signs by 

 which we know that something is going wrong and must 

 be remedied. 



