numerous folds in order to increase the secreting and absorbing surface (Fig. 96). On and between the folds are thousands of little threadlike projections called villi (Fig. 97). In each villus are found fine capillaries and a small lymphatic called a lacteal (colored Fig. 2). The villi are so thick that they make the lining of the intestine like velvet, and enormously increase the absorbing surface.
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Fig. 97.—Lining of Small Intestine, magnified, showing villi and mouths of intestinal glands.
Digestion in the Small Intestine.—This is by far the most active and important of the digestive organs. The mouth digests a small part of the starch, and the stomach digests a small part of the proteid; the small intestine digests most of the starch, most of the proteid, and all of the fats. The food is in the mouth a few minutes, and in the stomach two or three hours; it is in the small intestine ten or twelve hours. There are thousands of small glands called intestinal glands that open between the villi (Fig. 97) and secrete the intestinal juice, which digests cane sugar. Besides these, there are two very large and active glands, the pancreas and liver, which empty into the intestine by ducts.
The Pancreas.—The small intestine is the most important of the digestive organs, chiefly because it receives the secretion from the pancreas, the most important of digestive glands. The pancreas is a long, flat, pinkish gland situated behind the stomach (see Fig. 90). The pancreatic juice contains three powerful ferments, one of which (amylopsin) digests the starches, another (trypsin) digests proteids, and the third (steapsin), with the aid of the bile,
