PRINCIPLES OF FEEDING ANIMALS 315 



too, when confined and fed on corn, need ash, in the form 

 of ground bone and the like. 



Protein. In plants and animals most substances con- 

 taining nitrogen are called protein (pronounced pro'te in). 

 Forms of protein are the white of eggs and the curd in 

 soured milk. The protein of plants is used by the animal 

 to make lean meat, muscles, blood, and curd in milk. Men 

 or farm animals doing heavy work require an abundance 

 of this substance. So do cows when giving much milk. 

 Among the foods richest in protein are cotton-seed meal 

 and both the hay and the seeds of leguminous plants. In- 

 deed, seeds of all kinds contain a considerable proportion 

 of protein. 



Fuel for heat and force. The animal body is a ma- 

 chine with much work to do. Even an idle horse expends 

 some force or work in the circulation of the blood and 

 the digestion of food. All the work the horse has to do 

 increases the force or energy he must expend. Hence, 

 the horse needs to use a part of his food to produce force 

 or motion just as much as a steam engine needs burning 

 coal to furnish power. An animal needs some food to 

 serve as fuel to keep the body warm. Thus a part of the 

 food is consumed, or slowly "burned," in the body in 

 order to be changed into heat and force. Among the sub- 

 stances that serve as fuel to produce heat and force are 

 starch and sugar. Starch, sugar, and the coarse fiber of 

 plants are called car b5 hy'drates. This is because they 

 consist of carbon and hydrogen, in addition to oxygen. 



Fattening. An animal that digests more carbohydrates 

 than it needs for heat and force changes- the surplus into 



