A Practical Physiology: A Text-Book for Higher Schools

by Albert F. Blaisdell

The vital part of the tissues, built up from the complex classes of food, is oxidized by means of the oxygen carried by the arterial blood, and broken down into simpler bodies which at last result in urea, carbon dioxid, and water. Wherever there is life, this process of oxidation is going on, but more energetically in some tissues and organs than in others. In other words, the minutest tissue in the body is a source of heat in proportion to the activity of its chemical changes. The more active the changes, the greater is the heat produced, and the greater the amount of urea, carbon dioxid, and water eliminated. The waste caused by this oxidation must be made good by a due supply of food to be built up into protoplasmic material. For the production of heat, therefore, food is necessary. But the oxidation process is not as simple and direct as the statement of it might seem to indicate. Though complicated in its various stages, the ultimate result is as simple as in ordinary combustion outside of the body, and the products are the same.

The continual chemical changes, then, chiefly by oxidation of combustible materials in the tissues, produce an amount of heat which is efficient to maintain the temperature of the living body at about 98½° F. This process of oxidation provides not only for the heat of the body, but also for the energy required to carry on the muscular work of the animal organism.

225. Regulation of the Bodily Temperature. While bodily heat is being continually produced, it is also as continually being lost by the lungs, by the skin, and to some extent, by certain excretions. The blood, in its swiftly flowing current, carries warmth from the tissues where heat is being rapidly generated, to the tissues or organs in which it is being lost by radiation, conduction, or evaporation. Were there no arrangement by which heat could be distributed and regulated, the temperature of the body would be very unequal in different parts, and would vary at different times.

The normal temperature is maintained with slight variations throughout life. Indeed a change of more than a degree above or below the average, indicates some failure in the organism, or some unusual influence. It is evident, then, that the mechanisms which regulate the temperature of the body must be exceedingly sensitive.

The two chief means of regulating the temperature of the body are the lungs and the skin. As a means of lowering the temperature, the lungs and air passages are very inferior to the skin; although, by giving heat to the air we breathe, they stand next to the skin in importance. As a regulating power they are altogether subordinate to the skin.

Experiment 113. To show the natural temperature of the body. Borrow a physician’s clinical thermometer, and take your own temperature, and that of several friends, by placing the instrument under the tongue, closing the mouth, and holding it there for five minutes. It should be thoroughly cleansed after each use.

226. The Skin as a Heat-regulator. The great regulator of the bodily temperature is, undoubtedly, the skin, which performs this function by means of a self-regulating apparatus with a more or less double action. First, the skin regulates the loss of heat by means of the vaso-motor mechanism. The more blood passes through the skin, the greater will be the loss of heat by conduction, radiation, and evaporation. Hence, any action of the vaso-motor mechanism which causes dilatation of the cutaneous capillaries, leads to a larger flow of blood through the skin, and will tend to cool the body. On the other hand, when by the same mechanism the cutaneous vessels are constricted, there will be a smaller flow of blood through the skin, which will serve to check the loss of heat from the body (secs. 195 and 270).

Again, the special nerves of perspiration act directly as regulators of temperature. They increase the loss of heat when they promote the secretion of the skin, and diminish the loss when they cease to promote it.

The practical working of this heat-regulating mechanism is well shown by exercise. The bodily temperature rarely rises so much as a degree during vigorous exercise. The respiration is increased, the cutaneous capillaries become dilated from the quickened circulation, and a larger amount of blood is circulating through the skin. Besides this, the skin perspires freely. A large amount of heat is thus lost to the body, sufficient to offset the addition caused by the muscular contractions.

It is owing to the wonderful elasticity of the sweat-secreting mechanism, and to the increase in respiratory activity, and the consequent increase in the amount of watery vapor given off by the lungs, that men are able to endure for days an atmosphere warmer than the blood, and even for a short time at a temperature above that of boiling water. The temperature of a Turkish bath may be as high as 150° to 175° F. But an atmospheric temperature may be considerably below this, and yet if long continued becomes dangerous to life. In August, 1896, for instance, hundreds of persons died in this country, within a few days, from the effects of the excessive heat.