32 THE ARMY HORSE. 



The liver is the largest secreting organ in the body, weighing 

 from 10 to 12 pounds. It is situated inimediateh^ behind the 

 diaphragm and in front of the stomach. The liver secretes a 

 fluid called bile or gall which is emptied directly into the 

 small intestines, as the horse is not provided with a gall 

 bladder. 



The pancreas (sweetl>read) is situated behind the stomach 

 and in front of the kidneys. It is of reddish cream color, and 

 weighs about 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 effects some change in the blood, many 

 authorities claiming that it forms the white blood corpuscles 

 (see ''Blood"). 



The abdominal cavity is a large, somewhat oval cavity, 

 bounded above by the muscles of the back, below by the abdomi- 

 nal muscles, and in front by the diaphragm ; behind it is con- 

 tinuous with the pelvic cavity. The cavity is lined through- 

 out 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 de- 

 scribes the functions of parts of the digestive apparatus. 



Food, as it passes through the digestive or alimentary canal, 

 is subjected 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) remainder passes on and is discharged. 



The food, taken into the mouth by the lips, is masticated 

 (the mechanical first step) 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 converts them into sugar, which is more readily ab- 

 sorbed. This second step is called insalivation. 



