FEEDS AND FEEDING. 393 



SECTION LXII. PHYSIOLOGY OF DIGESTION AND 

 FOOD ECONOMICS. 



By DR. W. H. DALRYMPLE, 

 Department of Veterinary Science, Louisiana State University. 



That which an animal eats and drinks for the pur- 

 pose of nourishing its body, constitutes its food. Di- 

 gestion is the physiological process, or act, of changing 

 the food into soluble materials that may be absorbed, 

 or taken into the circulation and assimilated, or made 

 use of by the cells of the different tissues of which the 

 body is composed. 



The different steps in this physiological process are : 



1. Prehension, or seizing the food. This is accom- 

 plished in the horse by the lips and front teeth; in the 

 ox by the tongue, lower front teeth and dental-pad. 

 The dog prehends fluids by the tongue laps water, 

 for example. 



2. Mastication, or chewing, and insalivation, or mix- 

 ing the food in the mouth with saliva, from the differ- 

 ent salivary glands, which enters the mouth through 

 small ducts or tubes. 



Mastication is performed by the large back teeth, 

 molars, or grinders, which break up the grains and hard 

 particles; exposes them to the chemical action of a fer- 

 ment (ptyalin) of the saliva (which changes insoluble 

 starch into soluble sugar) ; and otherwise prepares 

 them for later steps in the digestive process, viz., in 

 the stomach, intestines, etc. 



3. Deglutition or swallowing. This step is accom- 

 plished by the aid of the tongue, certain muscles of the 

 throat, and the wave-like contractions of the oesopha- 

 gus or gullet, which carries the food into the stomach. 



In the ruminating animal, such as the ox, sheep and 

 goat, which " chew the cud," the food, in a somewhat 

 imperfectly-masticated condition, passes into the large 

 first compartment of the stomach (the rumen or 

 paunch), and then into the second (honeycomb or retic- 



