Nutrition may be defined as the sum of the processes concerned in the growth, maintenance, and repair of the living body as a whole or of its constituent organs.

An intelligent basis for the understanding of these processes is best acquired by a study of the organism when it is living at the expense of materials stored within itself, as it does in starvation.

Starvation or hunger is the deprivation of an organism of any or all the elements necessary to its nutrition. Thus when carbohydrates and fats only are eaten, protein hunger ensues. If the body is deprived of water or of calcium, thirst or calcium hunger, as the case may be, follows. Complete starvation occurs when all the required elements are inadequate. A fasting dog to whom no food or drink is offered does not undergo starvation in this sense, for the metabolized tissue furnishes enough water for the urine and respiration. There is also no water hunger in a dog when meat is ingested, for the meat contains enough water to dissolve the end-products of its metabolism in the urine. Dogs and cats have no sweat-glands in the skin except in the pads of their feet. They therefore are not so susceptible to water hunger as is man, whose body surface is constantly losing moisture.

A true picture of water hunger is presented by Straub,1 who gave a dog dry meat powder mixed with fat. Under these circumstances water is withdrawn from the tissues to dissolve the urea formed. He found that muscles may lose 20 per cent, of their water content without pathologic manifestations, although withdrawal of water somewhat increased the protein metabolism. The experiment could not be carried to the point of death from thirst, for after a few days the food was regularly vomited, on account of the decreased flow of the digestive secretions and an altered condition of the intestinal canal. The non-absorption of the meat powder threw the body on the resources of its own tissue, and this form of starvation, as has been shown, does not constitute water hunger.

1 Straub: "Zeitschrift fur Biologie," 1899, xxxviii, 537.

Rubner1 finds that starving pigeons die of thirst in four to five days, while those allowed only water live twelve days. Water hunger is, therefore, more quickly fatal than starvation when water is allowed. Under the usual conditions of so-called starvation experiments water is freely allowed, so that water hunger does not enter as a factor into the following discussion.

If water be available, the organism obtains the energy necessary for its continued existence from the destruction of its own store of protein and fat. After a variable length of time the organism succumbs. Exposure to cold greatly hastens the end. What is ordinarily called death from starvation is often really death from exposure.

Boldireff2 described rhythmic movements occurring in the empty stomach, and Cannon and Washburn3 have called attention to the intimate association of these contractions with the pangs of hunger. The subject has been studied in detail by Carlson4 in observations upon a boy with a gastric fistula. Twenty-four hours after a meal the stomach exhibited two types of rhythmic movements: (1) relatively feeble, but continuous contractions at the rate of three per minute, and (2) relatively strong contractions of the fundus, the true hunger-pains. The amplitude of these latter contractions shows a close correspondence with the intensity of the sense of hunger simultaneously registered. During strong contractions the knee-jerk was found to be exaggerated, indicating an increased tonus of the nervous system, and there was a great instability of vasomotor tone. Carlson suggests that this close association of the hunger-pains with the vasomotor center may be the cause of the faintness occurring in starvation. The hunger contractions and, in consequence, the hunger pangs are inhibited by: (1) the stimulation of the gustatory nerves through sweet, bitter, salt, and acid substances; (2) chewing any kind of substance, be it well or ill flavored or tasteless; (3) smoking; (4) swallowing movements. Water, coffee, tea, beer, wine, and brandy when taken into the stomach inhibit the movements and relieve the sense of hunger, though water is least effective in this regard.

1 Rubner: v. Leyden's "Handbuch der Ernahrungstherapie," 1903, p. 53.

2 Boldireff: "Archives des sciences biologiques," 1905, xi, 1.

3 Cannon and Washburn: "American Journal of Physiology," 1911-12, xxix, 441.

4 Carlson: "American Journal of Physiology," 1912-13, xxxi, 151.

Succi has fasted several times for thirty days. Dr. Tanner, an American physician, for forty days; and Merlatti, in Paris, for fifty days. Succi took laudanum in considerable quantity to stay the pain in his stomach, while Merlatti took only water.1 The effect of fasting on the spirits of the faster varies with the individual. Usually there is a loss of buoyancy of spirit, a decreased desire to work, and a decrease in the actual power of working. Succi, however, was capable of considerable exertion, such as walking and riding, without ill effects. A dog does not manifest the same depression as is seen in man. Dogs may be starved several days before they are run in a hunt. One of the longest fasts on record is that of Kumagawa's2 dog, which died on the ninety-eighth day. This dog was reduced in weight from 17 to 5.96 kilograms, a loss of 65 per cent.

A yet longer fast has been reported by Hawk,3 in which a dog fasted from February 6th to June 2d, a period of 117 days, 700 grams of water having been administered daily. The dog remained in "good spirits" during the whole fast, although its weight fell from 26.3 to 9.76 kilograms. There was no indication of a "premortal rise" in the nitrogen elimination in the urine. During the first four days of fasting the average nitrogen elimination in the urine was 6.23 grams or 0.23 gram per kilogram of body weight, and during the last four days it averaged 2.44 grams or 0.23 gram per kilogram. The dog then passed the summer upon a Kansas farm, fully regained his former weight, and in the autumn was reported to be in better physical condition than at the commencement of his fast. A second or "repeated fast" was then initiated which lasted 104 days with no harmful results.

1 Luciani: "Das Hungern," 1890, p. 28.

2 Kumagawa and Miura: "Archiv fur Physiologie," 1898, p. 431.

3 Howe, Mattill, and Hawk: "Journal of Biological Chemistry," 1912, xi, 103.

The day to day history of the starving organism must now be considered.