HEAT AND TEMPERATURE.

The average temperature of the human body in those internal parts which are more accessible, as the mouth and rectum, is from 98.5° to 99.5° F.

The chief circumstances by which the temperature of the healthy body is influenced are the following:

Age. The average temperature of the new-born babe is only about 1° F. above that proper to the adult. In old age the temperature rises again, and approaches that of infancy.

Sex. In the female slightly higher than in the male.

Exercise. Active exercise raises the temperature of the body, through muscular contraction, etc.

Climate and season. In passing from a temperate to a hot climate, the temperature of the human body rises slightly, rarely more than 2° to 3° F. In summer the temperature of the body is a little higher than in winter, ⅕° to ⅓° F.

Cold alcoholic drinks depress the temperature ½° to 1°F.

Warm alcoholic drinks, as well as warm tea and coffee, raise the temperature about ½° F.

In disease, as in pneumonia and typhus, it occasionally rises as high as 106° or 107° F.

In Asiatic cholera a thermometer placed in the mouth sometimes rises only to 77° or 79° F.

The temperature maintained by mammalia of an active state of life averages 101° F. In birds, the average is as high as 107° F., the highest temperature, 111.25°, being in the species of the linnets, etc.

The sources and distribution of heat. Wherever metabolism of protoplasm is going on, heat is being generated. All over the body heat is being set free; more abundantly in the more active tissues, and most of all in those tissues the metabolism of which leads to little or no external work. The metabolism of the tissues (including the blood) and of the food within the alimentary canal is the source of the heat of the body. But heat, being continually produced, is as continually being lost, as we have seen, by the skin, urine, and feces. The blood passing from one part of the body to another, and carrying warmth from the tissues where heat is being actively generated, to the tissues or organs where heat is being lost by conduction or evaporation, tends to equalize the temperature of the various parts and thus maintain a constant bodily temperature.

Taking the body as a whole, under normal conditions, the chief sources of the production of heat are the muscles, and the abdominal viscera, more especially the liver; and of these the liver deserves attention, inasmuch as it is always at work, whereas the heat produced by the muscles is at least largely dependent on their contracting, and they may remain at rest for a considerable period. The brain, too, may be regarded as a source of heat, since its temperature is higher than that of the arterial blood with which it is supplied.

Heat is lost by the skin, respiration, feces, etc. The great regulator, however, is undoubtedly the skin. The more blood passes through the skin the greater will be the loss of heat by conduction, radiation, and evaporation. The working of this heat-regulating mechanism is well seen in the case of exercise. Since every muscular contraction gives rise to heat, exercise must increase for the time being the production of heat; yet the bodily temperature rarely rises as much as a degree C., if at all. By exercise the respiration is quickened and the loss of heat by the lungs increased. The circulation of blood is also quickened, and the cutaneous vascular areas becoming dilated, a large amount of blood passes through the skin. The expenditure of heat may be tabulated thus:

By the skin, in conducting, radiating, and evaporating, 77.5per cent.
Warming expired air, 5.2per,, cent.,,
Evaporating the water of respiration, 14.5per,, cent.,,
In warming urine, etc., 2.6per,, cent.,,