The Amount of Food Required; the Classification of Foods; Standard Dietaries; Maintenance Diet; Relations of Diet to Various Conditions of Life; Practical Facts for Guidance; Dietary in the Tropics; Food Economics; Table of Food Values. The Physiologic Action of Moderate Doses of Alcohol; the Effect of Alcohol on the Muscular System; the Effect of Alcohol on the Nervous System. “If there is anything new of importance in the practice of medicine it is this modern work in nutrition.”—_Mendel_, 1914. The activities of animals are carried on by a certain expenditure of energy which is set free as the result of a chemical breaking down of the living tissues of the body. In order to maintain the equilibrium of the body this waste must be replaced by new material which is taken in the shape of food, drink, and oxygen. _Digestion_ is the term applied to those changes in the food-stuffs which precede absorption; it is a refining process which separates the useless from the useful, and further prepares the latter to be used as building-stones for the repair of organs and tissues and to furnish fuel to supply the motor energy of the body. In the human body the digestive processes are brought about by mechanical disintegration; by the action on the food-stuffs of acid and alkaline fluids; by changes produced by active substances called enzymes; and, lastly, decomposition is produced by the growth of microörganisms. The =digestive tract=, or alimentary canal, begins at the mouth and ends at the anus. It consists of the mouth, the esophagus or gullet, the stomach, the small and large intestines. Two large glands, the liver and pancreas, pour their secretions into the small intestine to aid in the digestion of foods. The alimentary canal, liver, and pancreas together constitute the digestive system. [Illustration: Fig. 4.—General scheme of the digestive tract, with the chief glands opening into it (Stockton). Nose Salivary (parotid) gland Salivary glands Pharynx Vein Trachea Thoracic or chyle duct Esophagus Liver Gall-bladder Stomach Spleen Pancreas Duodenum Lacteals Large intestine Small intestine Vermiform appendix Rectum ] The contraction of the muscular walls of the digestive tract is the propelling power that carries the food downward and brings it into contact with the digestive fluids. These movements will be referred to later, under the Mechanics of Digestion. The digestive tract is lined throughout its entire course by mucous membrane; that lining the mouth gives some idea of its character. It is from the mucous membrane lining the stomach and intestines, as well as from the liver and pancreas, that the digestive fluids are poured forth into its cavity.