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About the Book

Table of Contents

Part I

Part II

Part III

Part IV

Part V

Part VI

Part VII

Part VIII

     

Part V:  The Meaning of Sweat as Part of the Curse

Chapter 1

Animal and Human Sweating

     MOST OF US object to sweating particularly when others do it! Even the word itself is distasteful. Yet it is an absolutely vital function of the normal healthy body, and ectodermal displasiacs those unfortunate individuals who have impaired or inactive sweat glands are in a most dangerous situation. The slightest exercise or a rise in environmental temperature above what is called the "comfort zone" will endanger their lives very rapidly indeed. The resulting elevation of body temperature can occur in a very few minutes and reach fever heights, and there is absolutely nothing they can do about it except by using artificial cooling devices. In childhood such people (fortunately rare) have to be watched continually.
     So efficient, on the other hand, is the thermoregulatory mechanism of sweating in normal people that we seldom experience more than slight discomfort over a wide range of environmental temperatures, a fact which enables man to live anywhere on the earth. Indeed, for something like twenty minutes a man can survive temperatures as high as 260 degrees F high enough to broil a steak in the same cubicle with him, provided the air is absolutely dry so that all his sweat is evaporated.
     Under normal circumstances, the sweating mechanism is centrally regulated in the body through the hypothalamus. This "human thermostat," as Benzinger has called it, is so finely adjusted that a rise of only 0.01 degrees C in what is termed the deep body temperature results in a compensatory increase in thermal sweating for evaporative cooling equal to 1/1000 of a Calorie per minute. So, as Kuno (probably the world's greatest authority in this field) has said, a man is beautifully equipped physiologically to prevent any rise in body temperature.

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     Thermal sweat is one of the purest body fluids, containing less than 1 percent of substances other than water. It is completely odourless unless bacteria are allowed to grow in it. It can be copious indeed, and the weight loss via this avenue may be considerable without any injury to the subject. I have myself lost four pounds in one hour on a treadmill in our own laboratories! Since one gram of water evaporated removes 0.58 Calories of heat from the body, this hourly rate was ridding me of close to 1,000 Calories. In a crude kind of a way, this is equivalent to the heat energy of a good meal, all within one hour! Indeed, because the body produces this fluid secretion so readily during exercise, it can become a serious hazard in the Arctic: while dry clothing may be warm, wet clothing most certainly is not. Dr. Paul A. Siple of Antarctic renown pointed out to me the paradoxical truth that on this account the only way to keep warm in the Arctic is to keep cool!
     But in what way is man unique in this respect? Don't animals sweat profusely horses, for example? In spite of appearances to the contrary, animals are not equipped by nature as man is to achieve thermoregulation by sweating. The literature on this subject is voluminous. I have in my files a bibliography of at least three thousand works dealing with sweating, and this does not include a comparable literature to be found in other languages such as German, Russian, and Japanese. Sweating seems like such a simple, straightforward phenomenon; in reality it is a highly complex subject. Let us consider very briefly what we know about it, more particularly with reference to humans, drawing in part upon the thousands of experiments we have performed in our own laboratories over the past years, using soldiers as subjects.

     To begin with, we sweat for a number of different reasons, and this allows us to classify the reaction under at least six headings. There is thermal sweating which enables us to maintain a safe body temperature There is mental sweating, whose function is only partially understood but which is always found to parallel quite exactly the level of mental effort. Emotional sweating, as the name implies, occurs in response to excitement, fear, anxiety, and a multitude of other disturbed states. The omission of pain in this list of stimuli to emotional sweating is intentional; we shall discuss why subsequently. Another form of sweating is termed gustatory, resulting from the ingestion of highly spiced foods; its function is not clearly understood. There is also that

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reaction known as cold sweat, defined as a form of thermal sweating elicited by a non-thermogenic stimulus. It has been found to be a very dependable index of motion sickness. Finally there is sexual sweating, which is well established in animals and for which there is some evidence in humans. Undoubtedly other distinct types of sweating will be discovered in time, but these at least are known to be highly specific.
     The specificity of these types of sweating is not only associated with their innervation that is, their relationship to the central nervous system but also their location on the skin surface; briefly the situation is as follows: thermoregulatory sweat glands are distributed over the whole body surface except in a few restricted areas. Mental sweat glands are limited to the palms and soles, and more specifically to what are appropriately termed the contact points in these areas. Emotional sweat glands are found in the armpits, technically known as the axillae. Gustatory sweating is limited almost entirely to the facial area immediately surrounding the mouth. Cold sweating occurs over the whole body surface involving the thermoregulatory glands. Sexual sweating appears to be limited chiefly to the axillae, with some representation around the nipples and possibly in the pubic region.
     While these areas can be mapped with some measure of exactitude and labeled for the type of sweating which is characteristic of each, there are complications because in certain areas two different types may be found. Thus, in the palmar region sweating is elicited by mental stimuli such as occur when doing arithmetic, for example, and by emotional stimuli such as fear. There is, however, no response in spite of all appearances to the contrary to thermal stimuli per se. In the armpits sweating is elicited by emotional stimuli primarily, but also to some extent by thermal ones.
     For those who have not studied physiology, it may help for me to point out that there are two kinds of regulatory processes in the body: those which we can control to some extent (moving the eyes, the limbs, etc., and regulating the breathing), and those over which we have virtually no control (dilation of the pupil, alterations in the condition of the blood vessels relative to the volume of flow, movements of the intestinal tract in digestive processes, heart rate, etc.). It is difficult to be exact because some of these processes can be brought under control by training and others continue automatically until we decide to do something about them. 

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     However, a further division is made within the group of processes over which we have no control whatever under normal circumstances As a class these processes are called "autonomic" since they are self-regulating. Within this autonomic system there are those processes which prepare the body for flight or
fight (called "sympathethic") and those which prepare the body for recovery and restoration (called "parasympathetic"). Quite simply, the first class of activities includes an increased pulse rate and breathing rate, dilation of blood vessels leading to the muscles, dilation of the pupils, and a virtual cessation of digestive processes. The blood supply to the skin and to the digestive system is reduced. These preparatory and facilitative reactions are beautifully suited for the end in view, namely, to sharpen vision and to provide the muscles with maximum energy and more rapid removal of waste. One further process which occurs at the same time is the appearance of sweat in the palms and soles. Everyone is aware that dry hands reduce tactile sensitivity and frictional contact. The moistening of the hands provides better touch sense and grip: both facilitate action.
     When the occasion for flight or fight is passed, the body at once sets about restoring itself. Since, in the previous condition, it was essential to divert the blood to the muscles, a process facilitated by reducing the blood supply to the intestinal tract, the body did not waste food which had been ingested by allowing it to pass on through, but held it back so that the energy available in the food could be extracted when the time came for transfer to the blood. In the restoration period, the blood is once more supplied freely to the intestines and digestion is resumed. Blood is also diverted from the muscles to the skin surface in order to carry the body heat, elevated by increased metabolic activities, to the surface for cooling. This cooling process is assisted by the outbreak of sweat, which by means of evaporation removes the heat from the blood before it is returned once more to the heart. Thus thermal sweating is associated with recovery and restoration. Or, to put it in more technical language, mental and emotional sweating are sympathetic in origin, whereas thermal sweating is parasympathetic.
     In other words, while it may appear that sweating is a kind of universal reaction, the different kinds of sweating are actually quite differently controlled by the central nervous system and may work not only in entire independence but even in antagonism.

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     Let me give two illustrations of this. A person brought into an experimental laboratory who is not familiar with procedures, and who is to be subjected to a rising temperature in the room, may very quickly respond to the situation with an outburst of emotional sweating resulting from anxiety. Since the body is still cool enough, there will be no thermal sweating. As the temperature rises, however, in due time thermal sweating breaks out, but in the meantime the subject has become more at ease and mental and emotional sweating subside. However, if the room temperature is raised high enough so that the subject is distressed, emotional sweating breaks out once again. Throughout this whole process the course of these two different kinds of sweating in specific areas of the body can be measured and recorded continuously and are found to be virtually independent of one another.
     A second example is seen in the response of the sweat glands to a loss of consciousness as a subject goes to sleep or is anaesthetized. In normal sleep all mental sweating in the palmar regions ceases but, for reasons that are not well understood, there may be a considerable increase in the thermal sweating. The two curves cross over as they follow their entirely different course, the one declining as the other rises.
     In this brief survey of the subject, we have spoken of mental and emotional sweating as occurring together. This may not be so at all, each taking place independently. Thus mental arithmetic, as already mentioned, elicits mental sweating even in children without any necessary emotional component. Fright may induce emotional sweating in the axillae without any mental stimulation. Extreme fright may, in fact, block mental activity altogether.

     Just to keep the picture clear, we may summarize by saying that there are here three kinds of sweating: mental, emotional, and thermoregulatory. Sometimes these occur together, sometimes they occur independently. In some areas the glands appear to have the capability of sweating in response to two different kinds of stimuli:
in the palmar area, mental and emotional; and in the axillae, emotional and thermal. There is one unique area of the skin surface in which all three kinds of sweating may occur singly or together. This is in the forehead region. We return to this in the last chapter.
     Now, it should be emphasized that these different kinds of response do not result from the fact that the brain merely sends out an appropriate message and the gland reacts in an appropriate way, all messages travelling along the same lines of communication. In
reality there are different lines of communication (nerve pathways)  

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for the different kinds of sweating response. So any single area which can respond in two different ways probably has two different lines of communication, and these lines of communication do not originate in the same area of the brain nor do they leave the spinal cord at the same level. That one area the forehead region where three kinds of response are possible may perhaps be supplied with three systems of communication with the central nervous system. These anatomical features are not fully understood yet, and the authorities have by no means reached complete agreement. However, what has been said above regarding the innervation of the various types of sweat glands is sufficiently true to serve the purpose of making it very clear that these differences are not merely functional but anatomical also.
     With respect to animals, the situation is complicated because sweat gland function appears to serve the same object but in fact almost certainly does not. Thermoregulatory sweating in those animals which can be made to sweat in response to heat seems to be an unnatural phenomenon, and it is possible that the outbreak of sweat is not so much directed toward the prevention of a rise in body temperature (though it incidentally serves this purpose) as it is an indication of distress. The reason for believing this is that the sweat glands of horses, for example, are apocrine in nature, i.e., similar to the glands in the human axillae and are anatomically part of the sympathetic nervous system which, it may be remembered, does not provide for body cooling.
     Those who love beautiful animals (and I most certainly do) will object that a horse can sweat profusely and can then catch cold as a consequence. True, but there are two important observations to be made about this. First, sweating in horses is the result of exercise, not of a rise in body temperature. What triggers the sweat gland activity is a rise in adrenalin in the blood, not a rise in temperature in the body as a whole. The gland activity is not strictly thermogenic and only serves to cool the body by accident. Secondly, it is an inefficient system in any case, because the horse does not have any concurrent peripheral vasodilatation that would increase the transfer of heat to the skin surface, and its comparatively long hair makes even evaporative cooling inefficient. In nature, it is doubtful whether a horse ever sweats through the skin in order to maintain a normal body temperature. Sweating may possibly serve some other function, as a bactericide or fungicide on the skin, for example. It is analogous to the discomfort bordering upon pain which a high temperature may cause a

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human being, resulting in emotional sweating under the arms. Only a few animals actually sweat at all under normal circumstances in response to a rise in temperature. As one authority has pointed out, on a very hot, humid summer day it is the visitors at the zoo, and not the animals, who sweat. The sweating of horses is an exceptional circumstance, since it results from their being driven against their natural inclination to a level of exercise which they would otherwise most certainly avoid.
     It is a curious thing how frequently the theory of evolution has led to disappointing results when used as a guide in research. James Hardy, one of the most prominent physiologists to study the thermoregulation of the body, points out that at one stage of his research cebus monkeys were chosen as substitutes for humans in the belief that their thermoregulatory mechanisms would be much nearer those of humans than would other animals, such as the cat or dog. Research proved this to be quite wrong, the monkey being particularly poorly equipped to prevent a temperature rise. He concluded that "the cebus monkey is not a good experimental animal for bridging the gap between the data available on man and that available on animals as regards temperature regulation."
     What does appear from Hardy's work and from other sources is that the few animals that have some ability to prevent a temperature rise by evaporative cooling can be arranged in an ascending order of efficiency as follows. The monkey has virtually no ability, the cat has slight ability, the dog has greater ability still, the horse even more, and man almost complete. Somewhere between the dog and man must be placed cattle. The interesting thing here is that the ability to regulate body temperature by evaporative processes appears to increase according to the level of domestication enjoyed by the species, the monkey being least so, the cat next, and so on. Some dog lovers would claim greater domestication for the dog than the horse, but in those conditions under which sweating is likely to be necessary i.e., a high work rate the horse is undoubtedly better domesticated than the dog. Few would question that a harnessed horse is normally more completely tractable than a harnessed dog. I would conclude from all this that in nature no animal even begins to approach the level of physical efficiency of man's evaporative cooling system, least of all these particular monkeys.
    As we shall see, the uniqueness of man in this respect results partly from the fact that he is a fallen creature with a bodily efficiency
that is very low, probably not more than 20 percent. We shall examine later why he sweats on this account. 

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     Before we leave this general consideration of the subject, it may be of interest to note that animals have numerous ways of keeping themselves cool. Some small rodents are supplied with ample spittle and wash themselves thoroughly if they are feeling too warm, the evaporation of the spittle providing them with sufficient cooling. Some other small animals are supplied with a specially structured tail which acts as a heat exchanger when positioned in a certain way and allows them to reduce body heat. The sweat glands of dogs and similar creatures are in the mouth, and the rapid exchange of air in panting provides them with sufficient evaporative cooling. Prehistoric animals, like the dimetrodon, were equipped with a sail-like structure on the back which served probably as a heat exchanger, acting in two ways: to remove body heat in hot weather and to gain solar heat in the cold. Some animals make the adjustment by reducing basal metabolism, while others immerse themselves in water or burrow into the cool ground. Birds lift their wings slightly.
     Whatever the means, the fact remains that there are limitations which generally restrict the species to a certain temperature zone. Man is virtually free of such restrictions, partly by reason of his ability to produce an artificial environment by clothing and shelter, but also because of his ability to resist a temperature rise by copious sweating and the consequent evaporative cooling. Not infrequently this copiousness may seem to be wasteful. But a considerable body of evidence exists to show that the few elements which do exist in the sweat are of importance to man, since his body is thereby washed with a slightly acid solution which serves to protect him against bacteria and fungi. Unevaporated sweat, which seems to be an overcompensation and a pure waste of body fluid, turns out to have a value of its own. In the one area of the body where the acid might be dangerous to himself, namely, in the forehead region, the sweat is prevented from running down into his eyes by the eyebrows.

     As Scripture says, truly we are "wonderfully and fearfully made". 

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Copyright © 1988 Evelyn White. All rights reserved 

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