28 POWER AND THE PLOW 



horse's frame and weight are better disposed to dragging loads 

 over the surface of the ground. 



The fuel of the animal motor is in the shape of hay and grains. 

 These contain various heat-producing constituents which, in 

 order to become available as energy, must be transformed in 

 the animal body into muscular tissue. Of the various grains, 

 the horse can digest from 70 to 80 per cent, of the total nutrients. 

 However, of the coarser feeds such as hay and straw he 

 can recover only from 40 to 50 per cent., the remainder being 

 discarded without benefit to the animal, much as the cinders, 

 ashes, and unburned gases pass out of the steam engine with- 

 out being converted into heat. 



The food which is taken into the body of the animal is first 

 chewed fine and softened by mixing with from one to four times 

 its weight in saliva, to prepare it for the digestive juices of the 

 stomach. These juices, aided by ferments in the saliva and 

 in the food itself, start the work of reducing the nutrients in 

 the food to the soluble form in which they are taken into 

 circulation. The horse's stomach has a capacity of but 

 twelve to fifteen quarts, hence must be emptied several times 

 during a meal. The liver and the intestines, therefore, 

 perform a large part of the work of digestion. This process 

 of assimilation plays no small part in the total work of the 

 animal body. A horse's jaws, moving eighty times per minute, 

 will require from two and one half to three hours to chew the 

 hay ration. From five to six hours for oats and six to eight 

 hours for hay are required for the digestive organs to complete 

 their work. Frequently, as is the case of straw, the energy 

 required to chew and digest the food is greater than the energy 

 recovered from it. 



The various foodstuffs are composed of classes of compounds 

 known as proteids, fats, carbo-hydrates, ash and water. The 

 ash contains a small amount of mineral matter required in 

 the bony framework of the body, and the water is necessary 

 for the free action of the various bodily functions. Otherwise, 



