30 THE ARMY HORSE IN ACCIDENT AND DISEASE. 



17 ounces. Its function is to secrete pancreatic fluid, which is poured 

 into the small intestine. 



The spleen is situated on the left side of the stomach. It is pointed 

 at the lower end and gradually widens as it extends up to the region 

 of the left kidney. The spleen is of a reddish-gray color and in the 

 healthy horse weighs from 2 to 4 pounds. In disease, however, it 

 may reach an enormous size. 



The function of the spleen is not positively known, but it is believed 

 that this organ acts as a storehouse for the supply of blood to the 

 stomach during digestion and that it effects some change in the 

 blood, many authorities claiming that it forms the white blood cor- 

 puscles. (See "Blood.") 



The abdominal cavity is a large, somewhat oval cavity, bounded 

 above by the muscles of the ba»ck, below by the abdominal muscles, 

 and in front by the diaphragm; behind it is continuous with the 

 pelvic cavity. The cavity is lined throughout by a serous membrane 

 called the peritoneum. 



PHYSIOLOGY OF DIGESTION. 



By physiology is meant a description of the functions or uses of 

 certain structures. The physiology of digestion describes the func- 

 tions of parts of the digestive apparatus. 



Food, as it passes through the digestive or alimentary canal, is sub- 

 jected to a series of mechanical and chemical agencies by which it is, 

 in greater or less part, digested and worked up -to a condition in 

 which it can be absorbed by the appropriate vessels, and, while this 

 portion is taken up by the circulation, the effete (worthless) remain- 

 der passes on and is discharged. 



The food is taken into the mouth by the lips {preTiension) , where 

 it is ground up (mastication), and is mixed with saliva. Saliva, 

 secreted by the salivary glands in different parts of the head, acts 

 chemically upon the starchy components (parts) of the food and con 

 verts them into sugar, which is more readily absorbed. This step is 

 called insalivation. 



The next step, deglutition or swallowing, is mechanically per- 

 formed by the tongue, pharynx, and esophagus. 



When the food reaches the stomach it is subjected to the next 

 step, maceration, a mechanical rolling, mixing, and soaking with the 

 gastric juice. During maceration the gastric juice acts chemically 

 upon other components (nitrogenous parts), rendering them absorb- 

 able. Food in the condition in which it leaves the stomach is called 

 chyme. 



In the small intestines the villi take up the absorbable parts 

 already prepared, and the remaining nourishing parts are imme- 



