While at first thought, leanness appears to be the opposite of obesity only, it really consists in a relative or absolute super-oxidation at least of carbohydrates, as well as fats, and perhaps of proteins also, since the deposited fat is, to a large extent, derived from these sources. We may carry the analogy so far as to say that leanness exists in two degrees, corresponding to glycosuria and to alimentary obesity. The first degree is due to the fact that the exercise, fatigue, mental strain and the perspiration, exposure to cold and other causes of heat abstraction exceed the average intake of calories, so that while the individual may be very far from starvation, and may actually eat more than the average ration, his diet is too meagre to allow the deposition of more than minimum quantities of fat.

The second degree of leanness implies that on a diet considerably in excess of the theoretic demands of the body and with no detectable excess of digestive waste, the individual cannot deposit the normal amount of fat.

There is, strictly speaking, no third degree of leanness. While the patient may become emaciated from lack of food, from stricture of the oesophagus, from achylia totalis (as in Addison's disease) from malignant disease, diabetes etc., there is no essential metabolic condition in which the superoxidation of nutritive material not directly connected with deprivation or with suboxidation in other respects, threatens life or the maintenance of the ordinary functions of the body.

Leanness not directly connected with absolute or relative deficiency of food nor with some obvious pathologic explanation, is usually found in persons of tall and angular build, so that the opportunities for heat loss by evaporation and radiation are relatively great and the condition is, to some extent, a family tendency.

Some cases, especially in women, are relieved by increasing the amount of clothing habitually worn. Otherwise, the treatment consists in carefully increasing the diet, especially in carbohydrates and to some extent fats. Often it is advantageous to administer one or two light luncheons in addition to the regular meals. An abundance of sleep should be taken and mental worry should be reduced to a minimum. It is a mistake to attempt an excessive diet or to reduce the physical exercise unduly. Care should be taken to detect digestive errors, alimentary saprophy-tosis etc. In intrinsic cases, the prognosis with regard to increasing weight is not very good, but the health is or may usually be rendered excellent and with advancing years there is usually a tendency to take on flesh.