No food element is more important for the needs of the body than water. It is composed of oxygen and hydrogen. It forms the large part of the blood and lymph. The body will subsist for weeks on the food stored in its tissues; it will even consume the tissues themselves, but it would soon burn itself up without water, and the thirst after a few days without it almost drives one insane. Though it produces force only indirectly, it is entitled to be classed as a food, because it composes about two-thirds of the weight of the body and a large part of all the tissues and secretions. Yeo estimates that the supply of water to the body should be averaged at half an ounce for each pound of body weight. It has been estimated that from four to five pints of water are excreted each day by the body and therefore a similar amount should be consumed daily. The average individual at normal exercise, requires about seventy one and one half ounces of water daily, which equals about nine glasses (one glass of water weighs one-half pound). Some of this may be obtained from the food. By reference to Tables I to V it will be noted that water forms a large percentage of all food, particularly of green vegetables and fruits. In order that the body may do efficient work in digestion and in the distribution of the nutrient elements of the foods, and that the evaporation from the body may be maintained, the water in the foods, together with the beverages drunk, should consist of about seventy-five per cent. liquid to twenty-five per cent. nutrient elements, or about three times as much in weight as proteins, fats, and carbohydrates combined. Much of the water taken passes through the system without chemical change and is constantly being thrown off by the skin, lungs, kidneys, and intestines. Some of the water is split up into hydrogen and oxygen to unite with other substances in the chemical changes carried on during the process of digestion, and some water is obtained from the food by the union of hydrogen and oxygen liberated by the action of the digestive juices. Few people give much thought to its resupply; yet, ignorant of the cause, they suffer from its loss, in imperfect digestion and assimilation, and in kidney and intestinal difficulties. If it is withheld from the diet for a while, marked changes occur in the structure and processes of the body. The effect is seen in the lessening of the secretions, the increasing dryness of all the tissues, including the nerves, and if the lack is long continued, in progressive emaciation, weakness, and death. Water is the heat regulator of the body, and the more energy used, either in work or in play which results in more heat and evaporation, the more water is required. An animal, if warm, immediately seeks water. It is constantly being used in the body to form solutions in which the waste products are held so that the eliminative organs may dispose of them.