When the metabolism is perfect, any carbohydrates consumed in excess of the ordinary requirements are converted into glycogen and fat and stored for providing fuel at a future date. When stored as fats they are completely oxidized in the simplest compounds, carbon dioxid and water, and are eliminated through the lungs and skin, possibly part of the water so formed acting as a solvent for the urinary compounds. Investigations seem to prove that the body has a preference for the carbohydrates over fats or other nutrients as a source of energy. There is every justification for the abundance of starches in man’s diet. _Fat_ is essential in the food of mankind; it is absorbed ready formed from the food, or manufactured in the body from the proteins and carbohydrates. Neutral fats and fatty acids are valuable foods; their primary function is to supply the body with fuel for heat and energy. The _mineral substances_ form 5 or 6 per cent. by weight of the human body, and are constantly leaving it by different channels; they are indispensable elements of food. They give solidity and stability to the organism, constituting a considerable proportion of the bones. They keep various proteins in solution and confer upon them the property of electric conductivity. They are necessary for all of the secretions and assist in the general metabolism. The carbonates of soda, potash, iron, and other minerals render the blood and secretions alkaline. The removal of carbon dioxid is performed mainly by the alkaline carbonates, which take it from the blood and surrender it to the lungs. We have already considered the need of sodium chlorid. The total daily requirements of salts is estimated at about 360 grains. _Vitamins a New Factor in Nutrition._—But recent investigation has proved that something more is essential for the maintenance of growth and well-being than protein, carbohydrates, fats, and salts; that food contains a minute portion of accessory bodies, and that when they are deficient or absent from the diet the immature body does not grow, the mature body does not maintain its condition, and there are manifestations of more or less serious disease. These accessory bodies have been called “vitamins,” and they are essential to maintain the normal metabolism of the body. It is recognized that although vitamins are undoubtedly widely distributed in food products, they occur for the most part in very minute amounts, and the various foods differ in the proportion which they contain. If the diet is made up of substances which are poor in vitamins, or rendered so by their mode of preparation, abnormal metabolic processes have been found to follow.