The usual conception of obesity, particularly in the United States, is that it is always caused by an imbalance between intake and output of energy. "Exogenous or simple obesity is the result of maladjustments between food and exercise. Endogenous obesity is due to the lowered metabolism resulting from a disturbance in hypothalamic or endocrine functions, e. g., gonads, pituitary, or thyroid" (Best and Taylor,1 page 981).According to Means,2 both the exogenous and the endogenous type of obesity are due to a simple disproportion between the intake of food and the energy requirement of the body. Endogenous obesity is endogenous merely in the sense that in the creation of such a disproportion a fall in the rate of oxidation in the body plays a role. A much greater proportion of obesity, however, is of the exogenous type. As a matter of fact, the ratio between total caloric intake and total caloric output is what counts. Persons who gain weight readily, even though they appar¬ ently do not eat to excess, are usually phlegmatic ; they worry less, sleep either longer or more soundly and when at rest relax more com¬ pletely than persons of the normal, or thin, type. This conception of obesity has been substantiated chiefly by Newburgh and Johnston 3 and almost universally accepted on account of its pro¬ mulgation by leading authorities ; yet it is not satisfactory, for the fol¬ lowing reasons :•1. As nobody is in doubt that the law of conservation of energy holds also for the animal body and as it is an established fact that any surplus of intake of energy as compared with its output leads to accumulation of