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.
The secretion of the bile comes from the liver and the pancreatic juice from the pancreas or sweetbreads, and both are poured into the intestines near the same point, so that they act together. The ferments they contain act in the following ways: They change starch into sugar, fat into fatty compounds, they curdle milk, and convert protein compounds into soluble peptones.
The process of digestion is finally ended in the intestines, where absorption into the system takes place. There is no opening at all from the bowels into the body, but the digestive nutriment is picked up by the blood when handed into the body from the intestines by means of countless little cells called villi, that line the walls of the intestines. These villi cells have little hair-like projections extending into the intestines, which constantly move; these protrusions, as they move about, catch on to the digested nutriment, draw it into the cells themselves, where it is handed on to the blood, when it is later on distributed to all parts of the body. You can realize that an immense number of these absorption cells are present when the length of the intestine is considered. In the ox the intestine is nearly 200 feet long. After the nutriment is drawn from the food the undigested portions are voided periodically as feces or dung.
STOMACH OF RUMINANT
The four main divisions of the ruminant’s stomach are pictured here. The first three divisions are the store-houses for food until it is fully prepared for the fourth stomach or abomasum.