ANIMALS. 133 



Digestion. The purpose of digestion is to dissolve 

 food and change its nature, preparing it to enter the 

 blood, and to sustain the life and growth of the body. 

 As the food of plants is slowly prepared to enter the sap 

 by chemical processes in the soil, so the food of animals 

 is prepared in their digestive organs to enter the blood 

 by similar processes, although much more rapidly. 



The Mouth. The process of digestion begins in the 

 mouth. The food is not only ground into a fine condi- 

 tion by mastication, 

 and better- prepared 

 for chemical action, 

 but is also mixed with 

 the saliva. 



This is a liquid 

 consisting mostly of 

 water, but containing 

 substances suited to 

 produce some chemi- 

 cal action upon the 



. One of the Salivary Glands. 



food. It is secreted, 



or separated from the blood, by a number of organs 

 called glands, situated in different parts of the mouth. 

 As the blood passes through these glands, the saliva is 

 taken from it and poured into the mouth as it is needed 

 to moisten the food. It is formed quite rapidly while 

 the animal is eating. It is said to be produced in the 

 mouth of a horse or an ox, at such times, at the rate of 

 four quarts per hour. 



The Stomach and Intestines. After the food which has 

 been moistened by the saliva passes into the stomach, it 

 is mixed with other liquids, which are withdrawn from 

 the blood and poured into the stomach. 



