It is proposed in this chapter to describe briefly the processes of digestion. It is assumed that the reader is well acquainted with the structure of the digestive system, including a knowledge of the mucous lining of the alimentary canal throughout, and of the tributary digestive glands such as the salivary glands of the mouth; the gastric glands of the stomach wall; the pancreatic gland that lies behind the stomach and pours its secretion into the duodenum, and the liver, the largest glandular structure in the body, which occupies the upper right-hand portion of the abdominal cavity and pours its secretion, the bile, into the duodenum; the intestinal glands situated deeply in the walls of the small intestine, and the mucous glands of the large intestine. It is expected further that he is acquainted with the musculature of the walls of the alimentary canal, and the location of the sphincter muscles of cardia, pylorus, and anus. He is further expected to know the circulation of these parts of the digestive system, its immediate source and how it is distributed, also the innervation and the factors which influence through the nerves the muscular movements and secretory activities of the alimentary canal and its tributary glands. With this knowledge well in hand, we may proceed with a brief but sufficiently full consideration of the physiological processes of digestion.

It will be found that the knowledge of foodstuffs and foods, as set forth in the preceding chapters of this work, will be of the greatest assistance in understanding not only the nature of the digestive processes but their significance and their relation to general life processes, including nutrition.