Urges to eat and drink in rats.

Studies of nutrition usually depend upon the animal’s urges to eat and to drink. But little has been done to find what factors of the diet rn&l3y those urges. When body weight is employed as a measure of nutritive state, the observer ordinarily is assuming that intake has been sufficient to supply whatever is available. If weight has been lost he often assumes that the diet is inadequate qualitatively and not quantitatively. To what extent is this confidence in the urges toward maintenance justified? The following aspects of intake are here investigated: e$ect of dilution of food by roughage, effect of flavoring, effect of dilution of food by water, forcing of water intake by mixture of water with food, and after-effects of partial or complete privation of food, or of water, or of both. The investigation was designed to ascertain how an animal solves conflicts, and practices priorities, in its bodily maintenance. If it be obliged to ingest an excess of water while obtaining food, how much excess will it take? If more than the requirement of some constituent cannot be avoided, will the total intake be in excess of metabolic uses ? In general, how much excess of A in the diet will reduce or stop the intake of B? How are conflicts of metabolisms compromised, and do the urges of intake correspond to a pattern that favors maintenance of the individual,* without or with the connivance of the machinery of outputs? By answering such questions, even in part, the physiological organization of the animal body can be partially described. In a general way it is recognized (1) that mammals often gauge intakes according to certain nutritive values, in spite of inequalities of form and substance in various diets. But it is also known that some constituents of food or drink act as deterrents to ingestion, as is illustrated by substitution of sea water for fresh water (2). The investigation included attempts to induce rats to ingest, large quantities of water, simply by mixing the water with the food available to the animals. As a consequence, a general method was worked out of forcing into the metabolism of an animal considerable quantities of various ingested materials that would ordinarily be refused. Help in the experiments was received from M. C. Nudo, S. Parmington and M. M. Stiler. Aid in completing the investigation was derived from a contract between the Army Air Forces and the University of Rochester. Mixtures of food with roughage. What characteristics of foods may guide rats’ food consumption? Are the textbooks correct in suggesting that alimentary fill is a chief requirement of the animal? Male white rats were furnished first with an adequate dry food (chow) ad libitum, then later given the same food thoroughly mixed with a form of roughage (cellulose or kaolin). Water was