49 On account of the formation of carbon dioxide in places containing decaying material, the descent into an old well or other opening into the earth is often a hazardous undertaking. Before making such a descent the air should always be tested by lowering a lighted lantern or candle. Artificial respiration is the only means of restoring one who has been overcome by this gas (page 97). 50 While awaiting oxidation at the cells, the carbohydrates and fats are stored up by the body, the carbohydrates as glycogen and the fats as some form of fat. In this sense they are sometimes looked upon as serving to build up certain of the tissues. 51 The following table shows the main elements in the body and their relation to the different nutrients: [Nutrient Table] 52 The recently advanced theory that the molecules of the mineral salts, by dissolving in water, separate into smaller divisions, part of which are charged with positive electricity and part with negative electricity, has suggested several possible uses for sodium chloride and other mineral salts in the body. The sodium chloride in the tissues is in such concentration as to be practically all separated into its sodium and chlorine particles, or ions. It has recently been shown that the sodium ions are necessary for the contraction of the muscles, including the muscles of the heart. There is also reason for believing that the different ions may enter into temporary combination with food particles, and in this way assist in the processes of nutrition. 53 Chittenden, _The Nutrition of Man_. 54 Compiled from different sources, but mainly from Atwater’s _Foods: Nutritive Value and Cost_, published by the U.S. Department of Agriculture. 55 The calorie is the adopted heat unit. As used in this table it may be defined as the quantity of heat required to raise 1 kilogram (2.2 pounds) of water, 1 degree centigrade. The calories also show the relative amount of energy supplied by the different foods. 56 While alcohol cannot be classed as a food, it is believed by some authorities to contain _food value_ and, in the hands of the physician, to be a substance capable of rendering an actual service in the treatment of certain diseases. It might, for example, be used where one’s power of digestion is greatly impaired, since alcohol requires no digestion. But upon this point there is a decided difference of opinion. Certain it is that no one should attempt to use alcohol as food or medicine except under the advice and direction of his physician.