3 22 



THE ESSENTIALS OF AGRICULTURE 



addition, for the production of wool. Swine grow and fatten 

 rapidly, hence their greediness. Therefore, it would be absurd 

 to feed all kinds of animals in the same way and without regard 

 to the kind of product they manufacture. 



416. Digestion of feed. The feed must first be digested in 

 the animal body. Most digestive changes are due to the action 

 of the ferments, or enzymes, present in the digestive juices. 

 Each ferment produces its own peculiar results ; for example, 

 diastase converts starch into a form of sugar, pepsin renders a 

 part of the proteins of the food soluble, and lipase acts upon 



colon, or large intestine -^-. 



roof of mouth stomach 

 , Pharynx 



esophagus 



bile ducL 

 tongue ^salivary ducts 



pancreatic duct 



small intestine 



rectum anu.s 



colon, or large intestine 



FIG. 160. The digestive tract of a hog. (Diagram from Iowa State College) 



the fats of the food. Bacteria also play an important part in 

 digestion of food, attacking the food chiefly in the large intes- 

 tine. It is from the small intestine that most of the digested 

 material passes into the blood to be carried to the different 

 parts of the body. 



417. Organs of digestion. Digestion begins with mastication 

 and continues up to the time the undigested part of the food 

 leaves the body (Fig. 160). Most animals masticate or chew 

 their food as they eat it, and at the same time saturate the food 

 with saliva. Cattle and sheep chew their food only sufficiently 

 to allow it to be swallowed and remasticate it later. Fowls 

 swallow their food whole and grind it in their crops and giz- 

 zards (Fig. 161). The horse and the hog have comparatively 



