What has been said concerning the mastication of starches applies with almost equal force to other foods. Without exception their digestibility is much increased by thorough chewing. As the result of recent experiments carried out by means of the X-ray, it has been shown that particles of food of any considerable size will not pass from the stomach into the intestine; as often as an object of this kind attempts to force its way from the former into the latter the opening between the two closes, and as a consequence the food is retained in the stomach longer than it is in health--resulting in the course of time in catarrhal conditions of the organ just named, and an unnatural relaxation of its muscular walls. Under such circumstances the patient quickly develops symptoms of indigestion, and if his habits be not corrected the trouble gradually grows worse until the sufferer becomes a chronic dyspeptic. _Classes of Nutritive Substances._--All substances that are of any appreciable value in nutrition may be divided into those that are nitrogenous in character (albumins, legumins), the carbohydrates (starches and sugars) and compound ethers (fats). Of all these the nitrogenous foods are the most important, since they contain the material from which the great bulk of the body is largely composed, and at the same time there is every evidence that in case of need they may be broken up into chemical substances that may take the place of any of the other kinds of foods; upon nitrogenous food, then, a man may live alone, while this cannot be done on other articles of diet. The fats, starches and sugars are very closely related to each other, and it is generally believed that they subserve much the same end in the economy; by undergoing chemical change they furnish energy (heat and muscular force) and are undoubtedly largely responsible for the formation of the fats of the body. While there is some evidence that under certain conditions alcohol may be a food, its value is certainly very small, and it is not of sufficient importance to be considered in this connection. The ideal diet then for a healthy man is a proper proportion of nitrogenous (albuminous) food, along with a reasonable portion of fats, starches and sugars. Professors Voight and Atwater have calculated the following table, which fairly represents the amount of proteids, fats and carbohydrates that should compose the rations for twenty-four hours for the ordinary adult male. ADULT MALE OF AVERAGE WEIGHT. At Rest. Moderate Labor. Severe Labor. Proteids 110 grammes 118 grammes 145 grammes. Fats 50 " 50 " 100 " Carbohydrates 450 " 500 " 500 "