The Intake of Energy Remains the Same, but the Consumption of Energy Decreases.-As indicated above, the desire for food and the actual intake of food under altogether normal conditions correspond to the increase or decrease of energy consumption. Occasionally this natural regulatory process is interrupted; this is seen with particular frequency when individuals, who have been accustomed to taking much exercise, for some reason change their habits and begin to lead a more lazy life. In men following various callings, this frequently occurs towards the fifth decade of life or somewhat later. In women usually a decade earlier, when the children are no longer little and when a part of the domestic duties is assumed by grown-up daughters, housekeepers, and a larger corps of servants. Habits in regard to the amount of food that is eaten remain the same as in past years but less energy is consumed, so that what was formerly a maintenance diet now becomes a surplus diet; and these factors produce, either slowly or rapidly, an increase in the fat deposits of the body. External circumstances of this character are not the only cause that may lead to a more sedate method of life; disease, for instance, may force such a change in habits; I refer to disturbances about the circulatory and respiratory apparatus, or diseases of the nervous system, or of the organs of locomotion. There are innumerable such possibilities and it is very important that the physician should look for any influences of this kind. Very often a little well-directed advice that hits at the core of the difficulty, but at the same time does not too seriously interfere with the ordinary methods of life and the comfort of the patient, may restore the balance between the intake and the output of energy.

I designate all cases of obesity that originate in such a way that the intake of food is only of average size while the output of energy remains below the normal average as "obesity from inactivity." This expression is intended to indicate merely that the mus culature is too inactive; it is not intended to cast reflections upon the psychic attitude of these patients, for many of them are by no means deficient in mental energy; they are only prevented by disease, etc., from transforming it into actions.

It is clear that frequently the factors that predispose to "obesity from overfeeding" are combined with factors that predispose to "obesity from lack of exercise," so that the two reinforce one another.