Heat and the sensation of heat are two widely different states. When, on a chilly day or after washing in cold water, a man rubs his hands until a glow of heat seems to suffuse them, there is a very slight rise of actual temperature caused by the friction; the feeling is principally due to nerve-excitement, produced mechanically by the rubbing. The blood flows more freely into, and through, the parts excited immediately afterward, as shown by the redness, but the first impression of heat is mainly one of sensation. The feeling and the fact are not even constantly related. A person may feel hot when not only the surrounding temperature but that of his body is low; or, he may feel cold when really overheated. These perverted sensations are occasionally morbid—that is to say, form part of a state of disease—or they may arise from individual peculiarities which, perhaps, render perceptions of a particular class especially acute. On the other hand, there are conditions of the body, and special sensibilities, in which the sense of heat is dulled, and even considerable elevations of temperature are not perceived. It is easy to see how impossible it must be to form a correct judgment of the actual state of heat either around or within us by simple sensation. Throughout the world, whether man be placed in tropical heat or arctic cold, the temperature of his body must, to maintain health, be preserved at the same point—about 98.4 to .6 degrees of Fahrenheit. A very small departure from this universal mean standard constitutes or indicates disease. The external heat is comparatively unimportant, or only of secondary moment, in the economy of nature; we can not rely upon it for the compensation of differences in the heat generated within the body by the organism. Except for the production of a temporary effect, such as to give time for the reëstablishment of the normal temperature in a body chilled, as by submersion, external heat is useless for vital purposes. The only way in which it can act is by preventing the loss of more heat, and giving a slight aid to recovery by warming the surface of the body. If when a person is cold he goes into a heated apartment, or sits before a large fire, he receives with advantage just as much heat as will bring the skin of his body up to the normal standard; as soon as that point is reached, the organism will begin to labor to get rid of the superfluous caloric, and by sweating the heat must be kept from rising above the standard. All the heat thrust upon the body above 98.6 degrees is waste and mischievous except in so far as it may promote perspiration, which probably helps to work off some of the useless and burdensome, possibly morbid and poisonous, materials that oppress the system. This is how Turkish baths, and “sweatings” generally, do good, by exciting increased activity of the skin, and, as it were, opening up new ways of egress for matters which, if retained, might offend.