Whenever our body heat goes down more than five or six degrees, or up more than two or three degrees, then trouble at once begins.

If our temperature goes down, as from cold or starvation, we begin to be drowsy and weak, and finally die.

If, on the other hand, our temperature climbs up two, three, or four degrees, then we begin to be dizzy and suffer from headache and say we have "a fever." A fever, or rise of temperature, that can be noted with a thermometer, is usually due to disease germs of some sort in the body; and most of the discomfort that we suffer is really due more to the poisons (toxins) of the germs than to the mere increase of heat, though this alone will finally work serious damage.

However, as we well know from repeated experience, we need only to run or work hard in the sun for a comparatively short time to make ourselves quite hot enough to be very uncomfortable; and if we had no way to relieve ourselves by getting rid of some of this heat, we should either have to stop work at once, or become seriously ill.

This relief, however, is just what nature has provided for in this thick coat of blood vessels in our skin; it enables us to throw great quantities of blood out to the surface where it can get rid of, or, as the scientists say, "radiate," its heat.