ditions of exposure, first to heating and then to cooling influences. The principle of clothing should be to protect the body from external conditions which tend to abstract heat, when the surrounding temperature is lower than that of the body; and to strike heat into the organism, when the temperature of the outside air and of the substances with which the skin may be brought into contact is higher than that of the animal body itself.

The absorption of heat is determined by the degree in which the body is colder than the surrounding temperature. As we have said, no more external heat is wanted by the organism than will suffice to bring it up to 984 or 6° Fahr., and even this aid may readily be dispensed with if there be no abstraction or loss of heat from within. Practically therefore we do not need to absorb heat, and, in a temperate though changeful climate, are more deeply interested in keeping the heat we make in winter, and defending ourselves from the access of heat from without in summer by moderate measures, than in devising precautions against either extreme. Nature attaches more importance to internal heat that to variations of external temperature. She has given the inhabitants of the Torrid Zone dark skins because these are better for

the radiation of heat than white, although the dark colour absorbs more rapidly than the lighter. On the other hand, she has given the denizen of the Frigid Zone a pale skin, and clothed the Polar bear with a white fur because white does not so freely part with the heat it holds or covers, as black.

Radiation of heat takes place when the surroundings are cool, and, if the radiating body be a living animal organism, the aim must be to prevent too rapid dispersion. This points to the choice of materials and colours for clothing which hold the heat in winter, and of those which, so to say, resist it in summer. Reflection is in practice a part of radiation, except that the reflecting body may, in theory at least, be impervious to the heat it throws off from its surface, while that which, more strictly speaking, radiates must first have become charged with caloric. Evaporation is the great cooling process by which perspiration reduces the temperature of the body. When Nature covers the body with fluid the physical effect intended is the same which we produce artificially by sprinkling the surface of any object with water. In the act of passing off as vapour, the fluid takes away heat and thus cools the skin.

This is, in some measure, how sweating reduces the heat of the body in fever, and, in the absence

of a continuous cause of mischief or when the poison has done its baneful work and become exhausted, gives relief. The ancients used to think more of "critical sweatings" than modern physicians do; but it cannot be doubted that when a disease -of which excessive heat-production is a featureruns its course naturally, copious perspiration commonly occurs at the crisis, and the evaporation that follows helps to reduce the temperature. There are of course other natural methods by which the heat of the body may be reduced. For example, discharges of all kinds will carry off heat; but those from within generally take place when some large internal organ has been the seat of an accumulation of heating material which the system. has been unable to take up. For slighter ailments of the febrile order, surface-evaporation is generally preferred by Nature, and is commonly found to suffice.

Local temperature, that is, the heat in the several regions of the body is determined by conditions which control the circulation of the blood, and the function of nutrition or food appropriation. If the circulation is free in a part, its temperature is maintained; if, from any cause, the flow of blood is retarded, the local heat will be reduced. Any one may put this to the test by encasing the hands

in somewhat tight gloves when the weather is cold. The pressure prevents the free passage of the blood through the vessels, and the temperature falls. There is no warmth of any kind in the gloves; they act simply as non-conductors of heat, and prevent the heat generated within the body from passing off. For example-if a piece of lint or rag be dipped in cold water and laid on the skin, and a sheet of impervious or non-conducting material, such as india-rubber or thick flannel, is wrapped closely round, the heat of the body will raise the cold water to a temperature at which it will be given off as steam the moment the covering is removed. When the extremities are enclosed in thick or dense coverings, their temperature will depend on the amount of heat generated within them, and if the flow of blood through the vessels is arrested or retarded, nothing is gained, but everything lost, by the measures taken to protect them from the external cold.

This is a matter of the highest practical moment, and needs to be thoroughly understood. The feet cannot be kept warm unless the blood circulates freely in the extremities, and that will not be the case if the boot, shoes, or stockings are tight. These last-named articles of clothing are practically the worst offenders. A stocking encircling the foot

and leg closely and enveloping every part, with special pressure at the instep, around the ankle, and above or below the knees, must inevitably tend to oppose the circulation and so reduce the natural heat. The arteries which bring the blood to the extremity are set deeper than the veins that carry it back, and, as the latter are provided with valves which open towards the heart, it is too commonly supposed that the "support" afforded by the stocking will favour the return of blood more than it can impede the deeper supply-currents, and so help the circulation; but practically we know this is not the fact, for a tight stocking ensures a cold foot, and the chilliness of which many persons complain is mainly caused by the practice of gartering, and wearing stockings which constrict somewhere or everywhere.

There is a popular notion that if the feet are cold the head must be hot, and by keeping the extremities warm with wraps the "blood is drawn from the head," and its temperature reduced. Those who have on the one hand studied the phenomenon of fever, and on the other noted the physical condition of races and individuals who habitually leave the extremities unclothed, will know that this theory of the distribution of heat is only partially true. Heat depends on the due supply of nutrient ele