About
the Book
Table of Contents
Part I
Part II
Part III
Part IV
Part V
Part VI
Part VII
Part VIII
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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.
pg
1 of 8
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
pg.2
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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.
pg.3
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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.
pg.4
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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)
pg.5
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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
pg.6
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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.
pg.7
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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".
pg.8
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Copyright © 1988 Evelyn White. All rights
reserved
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