. Biology and human life. Biology. WORKING OVER THE BODY'S INXOME 133 Parotid gland. Blood vessels Sublingual The peptones resulting from stomach digestion differ from pro- teins chiefly in being soluble in water and capable of diffusing through membranes. As the changing of proteins into peptones goes on, the mixture in the stomach becomes more and more liquid and more and more acid. From time to time a quantity of the liquid passes into the intestine. After a while most of the contents of the stomach has been changed to a mixture having the consistency of a rather thick pea soup, and all of
. Biology and human life. Biology. WORKING OVER THE BODY'S INXOME 133 Parotid gland. Blood vessels Sublingual The peptones resulting from stomach digestion differ from pro- teins chiefly in being soluble in water and capable of diffusing through membranes. As the changing of proteins into peptones goes on, the mixture in the stomach becomes more and more liquid and more and more acid. From time to time a quantity of the liquid passes into the intestine. After a while most of the contents of the stomach has been changed to a mixture having the consistency of a rather thick pea soup, and all of it has passed on into the intestine. 111. The bowels or in- testines. Among the high- est animals the gut has two distinct divisions. The first is called the small intestine, and in human beings it is about one inch in diameter and about twenty-four or twenty-five feet long. This opens rather abruptly into the large intestine, which is about two inches in diam- eter and about five feet long {seej,k, Fig. 74). You have probably handled a piece of pig gut or calf gut, which is used as sausage casing. The wall of the intestine is thin and soft. The Hning carries very small glands, and the outer layer contains muscle cells. The muscle cells are ar- ranged in rings: when they contract they simply reduce the diameter of the intestine at any given point. The contraction starts at the forward end (nearest the stomach) and passes backward along the whole length of the small intestine, aided by longitudinal muscles. As a result of these contractions some of the thick mixture of food and digestive juices is moved along, Suhnaxillary Fig. 75. The salivary glands There are three sets of glands which produce saliva : the parotid, in the cheek, just in front of the ears; the submaxillary,under the angles of the jaw; and the sublingual, under the tongue. The more the food is chewed, the smaller are the particles into which it is broken, and the more thoroughly is the saliva mLxed with these pa
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