Food Intake and Hypothalamic Hyperphagia †

Animals eat different amounts of different diets, which implies that they recognize some quality or qualities of the diet. Both Cowgill' and Adolph1 were aware of this problem, but no one appears to have made a systematic attempt to define the dietary quality recognized by animals. Both of these workers were led to the opinion that their animals seemed to "eat for calories," i.e., for energy. However, the mechanisms by which animals achieve caloric balance have never been elucidated. Since Richter' has shown that a rat's eating is periodic, the total amount of food eaten must depend upon (i) the amount of food taken at each meal, and (ii) the frequency of meals. At the time of eating, some "intrinsic food factor"t must operate to produce a change in the animal which is the signal to the animal (conscious or unconscious) to stop eating. During this meal the intake of this factor up to a constant amount, or in an amount which will produce some constant change in the animal, will take precedence over other qualities of the diet. During the non-feeding interval some other change, or perhaps the same change in the opposite direction, must prompt the animal again actively to seek food. This concept does not imply that the factor is a specific component of the diet (in the chemical sense), although this possibility has not been ruled out. It seems perhaps more logical to expect that