x.] DIGESTION OF FOOD. 87 



group are constituted, can, on an emergency, contri- 

 bute matter for the maintenance of warmth. It is not, 

 however, their legitimate duty, and when it is per- 

 formed by them it is done at a sacrifice of economy. 



182. Before we proceed to notice the economical 

 use of food it will be desirable to outline in a very 

 brief manner, the very important changes which 

 food has to undergo, before it can be utilized for 

 the purpose of animal life. For this purpose we will 

 take cattle as the basis of our comments. A bullock 

 has four stomachs, of which the first, which is known 

 as the rumen, is the largest of ffieTseries; it is simply 

 used for receiving the fresh gathered food. Whilst 

 the food remains in this stomach, it receives moisture 

 from the saliva, which is passed down the gullet from 

 the salivary glands which secrete it. The structure of 

 this stomach keeps the food gently moving, and 

 thereby assists the softening of the food, and the 

 general action of the saliva. The preparation thus 

 commenced in the first stomach, enables the food to 

 pass into the second stomach, and as soon as the 

 animal is prepared to "rurmriate the food, or as it is 

 commonly called, "chew the cud," the food passes 

 again into the mouth, for the purpose of being more 

 thoroughly masticated or chewed. 



183. This mastication has to accomplish two 

 distinct objects, it has 



To reduce the food into a fine condition, and also 

 To bring it under the action of the saliva. 



It is necessary that the food should be reduced to a 

 very fine condition, in order that every portion of it 

 may be the more perfectly acted upon in the process 

 of digestion. By digestion we mean that action upon 

 the food, which prepafelflFTor being taken up in the 

 blood, and thus contributing to the growth of the animal. 

 But this mastication has also the duty of securing 

 the full action of the saliva upon the food. This 



