A Practical Physiology: A Text-Book for Higher Schools

by Albert F. Blaisdell

Animal Heat.

223. Animal or Vital Heat. If a thermometer, made for the purpose, be placed for five minutes in the armpit, or under the tongue, it will indicate a temperature of about 98½° F., whether the surrounding atmosphere be warm or cold. This is the natural heat of a healthy person, and in health it rarely varies more than a degree or two. But as the body is constantly losing heat by radiation and conduction, it is evident that if the standard temperature be maintained, a certain amount of heat must be generated within the body to make up for the loss externally. The heat thus produced is known as animal or vital heat. This generation of heat is common to all living organisms. When the mass of the body is large, its heat is readily perceptible to the touch and by its effect upon the thermometer. In mammals and birds the heat-production is more active than in fishes and reptiles, and their temperatures differ in degree even in different species of the same class, according to the special organization of the animal and the general activity of its functions. The temperature of the frog may be 85° F. in June and 41° F. in January. The structure of its tissues is unaltered and their vitality unimpaired by such violent fluctuations. But in man it is necessary not only for health, but even for life, that the temperature should vary only within narrow limits around the mean of 98½° F.

We are ignorant of the precise significance of this constancy of temperature in warm-blooded animals, which is as important and peculiar as their average height, Man, undoubtedly, must possess a superior delicacy of organization, hardly revealed by structure, which makes it necessary that he should be shielded from the shocks and jars of varying temperature, that less highly endowed organisms endure with impunity.

224. Sources of Bodily Heat. The heat of the body is generated by the chemical changes, generally spoken of as those of oxidation, which are constantly going on in the tissues. Indeed, whenever protoplasmic materials are being oxidized (the process referred to in sec. 15 as katabolism) heat is being set free. These chemical changes are of various kinds, but the great source of heat is the katabolic process, known as oxidation.

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.

A much higher temperature may be borne in dry air than in humid air, or that which is saturated with watery vapor. Thus, a shade temperature of 100° F. in the dry air of a high plain may be quite tolerable, while a temperature of 80° F. in the moisture-laden atmosphere of less elevated regions, is oppressive. The reason is that in dry air the sweat evaporates freely, and cools the skin. In saturated air at the bodily temperature there is little loss of heat by perspiration, or by evaporation from the bodily surface.

This topic is again discussed in the description of the skin as a regulator of the bodily temperature (sec. 241).

227. Voluntary Means of Regulating the Temperature. The voluntary factor, as a means of regulating the heat loss in man, is one of great importance. Clothing retards the loss of heat by keeping in contact with it a layer of still air, which is an exceedingly bad conductor. When a man feels too warm and throws off his coat, he removes one of the badly conducting layers of air, and increases the heat loss by radiation and conduction. The vapor next the skin is thus allowed a freer access to the surface, and the loss of heat by evaporation of the sweat becomes greater. This voluntary factor by which the equilibrium is maintained must be regarded as of great importance. This power also exists in the lower animals, but to a much smaller extent. Thus a dog, on a hot day, runs out his tongue and stretches his limbs so as to increase the surface from which heat is radiated and conducted.

The production, like the loss, of heat is to a certain extent under the control of the will. Work increases the production of heat, and rest, especially sleep, lessens it. Thus the inhabitants of very hot countries seek relief during the hottest part of the day by a siesta. The quantity and quality of food also influence the production of heat. A larger quantity of food is taken in winter than in summer. Among the inhabitants of the northern and Arctic regions, the daily consumption of food is far greater than in temperate and tropical climates.

228. Effect of Alcohol upon the Lungs. It is a well recognized fact that alcohol when taken into the stomach is carried from that organ to the liver, where, by the baneful directness of its presence, it produces a speedy and often disastrous effect. But the trail of its malign power does not disappear there. From the liver it passes to the right side of the heart, and thence to the lungs, where its influence is still for harm.

In the lungs, alcohol tends to check and diminish the breathing capacity of these organs. This effect follows from the partial paralyzing influence of the stupefying agent upon the sympathetic nervous system, diminishing its sensibility to the impulse of healthful respiration. This diminished capacity for respiration is clearly shown by the use of the spirometer, a simple instrument which accurately records the cubic measure of the lungs, and proves beyond denial the decrease of the lung space.

“Most familiar and most dangerous is the drinking man’s inability to resist lung diseases.”—Dr. Adoph Frick, the eminent German physiologist of Zurich.
“Alcohol, instead of preventing consumption, as was once believed, reduces the vitality so much as to render the system unusually susceptible to that fatal disease.”—R. S. Tracy, M.D., Sanitary Inspector of the N. Y. City Health Dept.
“In thirty cases in which alcoholic phthisis was present a dense, fibroid, pigmented change was almost invariably present in some portion of the lung far more frequently than in other cases of phthisis.”—Annual of Medical Sciences.
“There is no form of consumption so fatal as that from alcohol. Medicines affect the disease but little, the most judicious diet fails, and change of air accomplishes but slight real good.... In plain terms, there is no remedy whatever for alcoholic phthisis. It may be delayed in its course, but it is never stopped; and not infrequently, instead of being delayed, it runs on to a fatal termination more rapidly than is common in any other type of the disorder.”—Dr. B. W. Richardson in Diseases of Modern Life

229. Other Results of Intoxicants upon the Lungs. But a more potent injury to the lungs comes from another cause. The lungs are the arena where is carried on the ceaseless interchange of elements that is necessary to the processes of life. Here the dark venous blood, loaded with effete material, lays down its carbon burden and, with the brightening company of oxygen, begins again its circuit. But the enemy intrudes, and the use of alcohol tends to prevent this benign interchange.

The continued congestion of the lung tissue results in its becoming thickened and hardened, thus obstructing the absorption of oxygen, and the escape of carbon dioxid. Besides this, alcohol destroys the integrity of the red globules, causing them to shrink and harden, and impairing their power to receive oxygen. Thus the blood that leaves the lungs conveys an excess of the poisonous carbon dioxid, and a deficiency of the needful oxygen. This is plainly shown in the purplish countenance of the inebriate, crowded with enlarged veins. This discoloration of the face is in a measure reproduced upon the congested mucous membrane of the lungs. It is also proved beyond question by the decreased amount of carbon dioxid thrown off in the expired breath of any person who has used alcoholics.

The enfeebled respiration explains (though it is only one of the reasons) why inebriates cannot endure vigorous and prolonged exertion as can a healthy person. The hurried circulation produced by intoxicants involves in turn quickened respiration, which means more rapid exhaustion of the life forces. The use of intoxicants involves a repeated dilatation of the capillaries, which steadily diminishes their defensive power, rendering the person more liable to yield to the invasion of pulmonary diseases.[^[38]]

230. Effect of Alcoholics upon Disease. A theory has prevailed, to a limited extent, that the use of intoxicants may act as a preventive of consumption. The records of medical science fail to show any proof whatever to support this impression. No error could be more serious or more misleading, for the truth is in precisely the opposite direction. Instead of preventing, alcohol tends to develop consumption. Many physicians of large experience record the existence of a distinctly recognized alcoholic consumption, attacking those constitutions broken down by dissipation. This form of consumption is steadily progressive, and always fatal.

The constitutional debility produced by the habit of using alcoholic beverages tends to render one a prompt victim to the more severe diseases, as pneumonia, and especially epidemical diseases, which sweep away vast numbers of victims every year.

231. Effect of Tobacco upon the Respiratory Passages. The effects of tobacco upon the throat and lungs are frequently very marked and persistent. The hot smoke must very naturally be an irritant, as the mouth and nostrils were not made as a chimney for heated and narcotic vapors. The smoke is an irritant, both by its temperature and from its destructive ingredients, the carbon soot and the ammonia which it conveys. It irritates and dries the mucous membrane of the mouth and throat, producing an unnatural thirst which becomes an enticement to the use of intoxicating liquors. The inflammation of the mouth and throat is apt to extend up the Eustachian tube, thus impairing the sense of hearing.

But even these are not all the bad effects of tobacco. The inhalation of the poisonous smoke produces unhealthful effects upon the delicate mucous membrane of the bronchial tubes and of the lungs. Upon the former the effect is to produce an irritating cough, with short breath and chronic bronchial catarrh. The pulmonary membrane is congested, taking cold becomes easy, and recovery from it tedious. Frequently the respiration is seriously disturbed, thus the blood is imperfectly aërated, and so in turn the nutrition of the entire system is impaired. The cigarette is the defiling medium through which these direful results frequently invade the system, and the easily moulded condition of youth yields readily to the destructive snare.

“The first effect of a cigar upon any one demonstrates that tobacco can poison by its smoke and through the lungs.”—London Lancet.
“The action of the heart and lungs is impaired by the influence of the narcotic on the nervous system, but a morbid state of the larynx, trachea, and lungs results from the direct action of the smoke.”—Dr. Laycock, Professor of Medicine in the University of Edinburgh.