The food, after being ground and mixed with the saliva fluid, goes to the stomach. With the horse and hog the stomach is a single sac not capable of holding very large quantities of food; with the cow and sheep, on the other hand, we find a large storehouse for holding food--a storehouse that is divided into four compartments, the rumen or paunch, reticulum, omasum, and the abomasum. The first three communicate with the gullet by a common opening. The cud is contained in the first and second stomachs, and, after it has been masticated a second time, it passes to the third and fourth, and to the bowels, where the process of digestion is continued.
The kidney of the hog is pictured here. As a rule it is usually impossible to diagnose kidney troubles in hogs and similar lower animals.]
=Gastric Juice.=--From this it will be noticed that chewing the cud is an act in the process of digestion; it refers only to rechewing the food so as to get it finer and better ground for digestion. While in the stomach the saliva continues the digestion of the starchy matter and is assisted by the gastric fluid that pours in from the lining of the stomach, which converts the protein or albuminoids into peptones. The fatty matter is not acted upon at this point. There are three constituents of gastric juice, which affect the changes in the food. These are pepsin, rennet, and acid. With rennet you are acquainted. It is used in the kitchen, in the making of cheese, and is obtained from the stomach of calves or other young animals. Pepsin, also obtained directly from the stomach, is now a conspicuous preparation in medicine. The food, after leaving the stomach, goes into the bowels and is acted upon by secretions of the liver and pancreas or sweetbreads. It should be noted in passing that no secretion enters the first three divisions of the ruminant’s stomach. It is only in the fourth or true stomach that the gastric juice is found.
=The Stomach Churn.=--While food is in the stomach it is subjected to a constant turning movement that causes it to travel from the entrance to the exit or intestines. When it passes into the small intestines it is subjected to the action of bile and pancreatic juices, which have principally to do with the breaking up of the fat compounds. Both resemble, to a certain extent, saliva in their ability to change starch into sugar.