That, however, animals may take on fat which varies in character is well known to breeders of cattle.  “The art of breeding and feeding stock,” says Dr. Letheby,[9] “is to overcome excessive tendency to accumulation of either surface fat or visceral fat, and at the same time to produce a fat which will not melt or boil away in cooking.  Oily foods have a tendency to make soft fats which will not bear cooking.”  Such differences are also seen between English and American bacon, the former being much more solid; and we know, also, that the fat of different animals varies remarkably, and that some, as the fat of hay-fed horses, is readily worked off.  Such facts as these may reasonably be held to sustain the popular creed as to there being bad fats and good fats, and they teach us the lesson that in man, as in animals, there may be a difference in the value of the fats we acquire, according as they are gained by one means or by another.

The recent researches of L. Langer have certainly shown that the fatty tissues of man vary at different ages, in the proportion of the fatty acids they contain.

I have had occasion, of late years, to watch with interest the process of somewhat rapid but quite wholesome gain in flesh in persons subjected to the treatment which I shall by and by describe.  Most of these persons were treated by massage, and I have been accustomed to question the masseur or masseuse as to the manner in which the change takes place.  Usually it is first seen in the face and neck, then it is noticed in the back and flanks, next in the belly, and finally in the limbs, the legs coming last in the order of gain, and sometimes remaining comparatively thin long after other parts have made remarkable and visible gain.  These observations have been checked by careful measurements, so that I am sure of their correctness for people who fatten while at rest in bed.  The order of increase might be different in people who fatten while afoot.

Facts of this nature suggest that the putting on of fat must be due to very generalized conditions, and be less under the control of local causes than is the nutrition of muscles, for, while it is true that in wasting from nerve-lesions the muscular and fatty tissues alike lessen, it is possible to cause by exercise rapid increase in the bulk of muscle in a limb or a part of a limb, but not in any way to cause direct and limited local increment of fat.

Looking back over the whole subject, it will be well for the physician to remember that increase of fat, to be a wholesome condition, should be accompanied by gain in quantity and quality of blood, and that while increase of flesh after illness is desirable, and a good test of successful recovery, it should always go along with improvement in color.  Obesity with thin blood is one of the most unmanageable conditions I know of.