The composition of the ash of different food materials varies widely, both in amount, and form of the individual elements. When for any reason it is necessary to increase the phosphates in a ration, milk and eggs do this to a greater extent than almost any other foods. Common salt, or sodium chloride, is one of the most essential of the mineral constituents of the body. It is necessary for giving the blood its normal composition, furnishing acid and basic constituents for the production of the digestive fluids, and for the nutrition of the cells. While salt is a necessary food, in large amounts, as when the attempt is made to use sea water as a beverage, it acts as a poison, suggesting that a material may be both a food and a poison. When sodium chloride is entirely withheld from an animal, death from salt starvation ensues. Many foods contain naturally small amounts of sodium chloride.
4. Organic Matter.--That portion of a food material which is converted into gaseous or volatile products during combustion is called the organic matter. It is a mechanical mixture of compounds made up of carbon, hydrogen, oxygen, nitrogen, and sulphur, and is composed of various individual organic compounds, as cellulose, starch, sugar, albumin, and fat. The amount in a food is determined by subtracting the ash and water from 100. The organic matter varies widely in composition; in some foods it is largely starch, as in potatoes and rice, while in others, as forage crops consumed by animals, cellulose predominates. The nature of the prevailing organic compound, as sugar or starch, determines the nutritive value of a food. Each has a definite chemical composition capable of being expressed by a formula. Considered collectively, the organic compounds are termed organic matter. When burned, the organic compounds are converted into gases, the carbon uniting with the oxygen of the air to form carbon dioxide, hydrogen to form water, sulphur to form sulphur dioxide, and the nitrogen to form oxides of nitrogen and ammonia.
5. Classification of Organic Compounds.--All food materials are composed of a large number of organic compounds. For purposes of study these are divided into classes. The element nitrogen is taken as the basis of the division. Compounds which contain this element are called nitrogenous, while those from which it is absent are called non-nitrogenous.[2] The nitrogenous organic compounds are composed of the elements nitrogen, hydrogen, carbon, oxygen, and sulphur, while the non-nitrogenous compounds are composed of carbon, hydrogen, and oxygen. In vegetable foods the non-nitrogenous compounds predominate, there being usually from six to twelve parts of non-nitrogenous to every one part of nitrogenous, while in animal foods the nitrogenous compounds are present in larger amount.