[Concluded.]
Now the clear, transparent air permits heat to be shot off, or rayed
through it with great freedom. But it does not readily receive heat “by
conveyance,” so long as it is still. If you put your hand into still
air which is as cold as a cold metal knob, you do not know that the
air is so chill as the metal, because it does not make your hand so
cold. The heat is not conveyed away from your hand as quickly. When air
is _moving_, instead of being still, the case is, however, altogether
altered. A current of air, or wind, carries away heat from warm bodies
very quickly as it blows over them. It does so because each fresh
little particle of air which is pressed against them, receives its own
share of the heat, and conveys it away, leaving fresh particles to come
up in their turn, and do the same thing. A pint of boiling water in a
metal pot placed in a strong wind having fifty degrees of heat, would
lose all its excess of heat as soon again as it would if standing in
still air having the same warmth. The old plan of cooling hot tea or
broth by blowing it, is correct in principle, though not in accordance
with good taste.
The laboratory of the living animal body has the supply of its fuel,
and the capacity of its air-blasts, so arranged that just about as
much heat is supplied through its internal furnace, as is lost from
its surface by “raying off” and “conveyance,” when the surrounding air
has a warmth of sixty degrees of the heat scale, and when its surface
is somewhat protected by a light covering of clothing, to lessen the
rapidity with which the heat is shot off and conveyed away. The heat is
then produced as rapidly in the internal furnace, as it is thrown off
from the outer surface, and the consequence is that the animal _feels
comfortably warm_. It only feels uncomfortably _hot_, when more heat is
produced in the furnace of the living laboratory than can be scattered
through its surface. And it only feels uncomfortably _cold_ when more
heat is scattered from the surface than can be kept up through the
burning of the inner furnace.
But in winter time the cold external air carries away heat much more
quickly from the surface of living animals, than the warmer external
air does in summer time. Here, then, is a little difficulty to be met,
if the warmth of the body is to be kept precisely the same in both
seasons. It is requisite that it should be always maintained at the
same point, because that point is the one which is most suitable for
the operations which are being carried on in the vessels and chambers
of its laboratory. Nature has two distinct ways in which she insures
this end.
In the first place, are you not aware that you get more hungry in
winter than you do in summer time? All living animals have pretty much
the same experience as yourself in this particular, and the reason
is that nature intends, during the cold season, to have more fuel
introduced into the supply-pipes of the body for the warming of its
structures. The furnace of the laboratory gets quickened in a small
degree; its slow fires are fanned into slightly increased activity,
more fuel is burned, and so more heat is generated to meet the greater
demand for it, dependent on the influence of the external cold.
But nature also thickens the clothing of animals during the cold
season, and so affords increased obstruction, through which the
escaping heat has to force its way. Have you not observed the sleek
silky coat which the horse wears through the summer, and then noticed
at the beginning of winter how this sleek coat is exchanged for a
thick, fuzzy shag, that looks more like wool than hair? The warm
winter coat economizes the heat produced in the furnace of the living
body, and keeps it from being scattered to waste as quickly as it is
through the sleek summer coat. This is nature’s other plan of meeting
the difficulty brought about by the changing temperature of the air.
Nearly all animals belonging to temperate and cold climates have this
change of apparel provided for them in spring and autumn, but in some
cases the change is rendered very striking in consequence of a summer
garment of bright gay colors being replaced by a winter one of pure and
spotless white. The fierce tyrant of the ice land himself, the polar
bear, has a dingy yellow coat during the summer, but puts on furs as
snowy as his own realms when once the summer sun has disappeared. These
white winter furs are always warmer than dark ones. Birds which do not
migrate to warmer regions of the earth in the cold season, have winter
and summer suits of apparel, just in the same way as quadrupeds. In
the winter a lining of the thick, soft white down is added beneath the
outer feathers. There is one little bird which comes to England in the
late autumn, driven there by the still greater cold further north, and
which is familiarly known as having two remarkably different costumes
for his English and his foreign residence. In England the snow-bunting
appears with a white body and tail, but abroad and in summer time he is
distinguished by a brilliant black tail and back, and a body and head
of pure white.
Man follows the example which nature has set before him, in the matter
of clothing. He prepares himself stout warm garments for winter time,
and thin cool ones for the summer; and not only this; in the hottest
regions of the earth, where there is most sunshine, he commonly goes
nearly naked, while in the coldest regions, near the poles, he puts on
the heaviest and warmest woolens and furs that he can procure. Now this
is one reason why man has been _apparently_ so uncared for by nature in
the particular of clothing. The seeming indifference and carelessness
is really consideration of the highest kind. All the different races
of the lower animals have their own narrow tracts assigned them for
their residence. In these tracts there is no very extreme diversity
of temperature, and provision is therefore easily made to adapt their
clothing to it just so far as is required. The human race, on the other
hand, is intended to cover the entire earth, and to subdue it; to
spread itself from the burning tropics to the frigid poles. The heat
which has to be borne in the tropics, is as much greater than that
which is experienced near the poles in winter time, as boiling water
is hotter than ice. At the poles, one hundred degrees of frost often
occur. In India, there are occasionally one hundred and thirty degrees
of heat under the canvas of tents. It therefore becomes an affair
of almost absolute necessity, that the skin of the widely scattered
lords of creation should be as unencumbered as possible, and that warm
clothing should have to be prepared and added as a covering whenever
circumstances call for its use. The head only, of the human being, has
a natural fur garment. This part of the body is covered with hair,
because the most delicate portion of the entire frame, the brain, is
contained within it. The skull is protected by hair, that the brain may
not be hurt by too sudden a change from cold to heat, or from heat to
cold.
There is another advantage attending upon the arrangement which has
left human beings dependent upon an artificial supply of clothing,
and which has ordained that they shall come into the world with naked
skins. In consequence of this arrangement it is very easy to secure
that amount of cleanliness which is necessary for the preservation of
the health of such delicately framed creatures. The artificial clothes
can be altogether changed at will, and they can be washed and aired,
as they never could be if they were inseparably attached to the skin.
Then, too, they can be removed from the skin in the early morning, or
at convenient intervals, and its surface can be thoroughly cleansed
and purified by bathing with water. Just think of the difference of
going into a bath of refreshing water unencumbered by clothes, and
of doing the same with thick, dabby garments clinging about you, and
having to shake yourselves like great Newfoundland dogs when you come
out; and also recall to mind the pleasure you experience every time
you change soiled linen for clean, and you will become sensible of how
much you owe to beneficent nature for having left you destitute of the
feathers of the bird, or the fur of the bear. The extreme importance of
making a fair use of this privilege has been already alluded to in its
proper place.
But nature has effected yet another very bountiful provision for the
comfort and safety of her tender charge, the living human animal. Even
when only covered by very light clothing, it is possible human beings
may be placed in air which is so warm, that heat is not carried off
from their bodies so fast as it is produced in the interior furnace.
In India, it sometimes happens that the air gets to be even hotter
than the living body. All movement of the air, then, heats, rather
than cools. Under such circumstances, nature adopts a very effectual
course to prevent warmth from collecting more and more in the frame,
until a disagreeable and injurious amount has been reached. Having
first reduced the supply of fuel to the smallest limits consistent
with keeping the fire going, by lessening the appetite, and by taking
away the craving for heating food, and having given a hint to adopt
such outer coverings for the body as are as little obstructive of the
passage of heat as possible, the heat drenches the surface of the
frame abundantly with moisture, which has the power to cool by its
ready evaporation. Take a small piece of wet linen and lay it upon
your forehead, or upon your arm, leaving it freely exposed to the air,
and you will find, that as the moisture evaporates from the linen,
your skin underneath will feel colder and colder. The heat of the
skin is used up in converting the moisture of the linen into steam,
exactly as the heat of a fire is used up in converting the water of
a kettle into steam when this is made to boil. The steam flies away
with the warmth of the skin very rapidly, and consequently the skin
soon comes to feel cold. Now, when the body gets to be very warm, and
the over-heated blood is rapidly pouring through the channels of its
supply pipes, then the three millions of little holes or pores, which
lie upon its surface, are opened, and floods of vapor and water are
poured through them, producing just the same kind of effect as wet
linen would do. This action is termed “perspiration,” or a “steaming
through” the pores of the skin. The breathing blows up, or fans the
slow furnace contained within the living animal frame, and so heats it
above the surrounding air. The perspiration carries away portions of
this heat when it has been raised too high, and so cools the heated
body down. Some moisture also escapes as steam from the lungs and
through the mouth in breathing, thus assisting the perspiring skin in
its office of diminishing the excessive warmth of the body. You have
often seen dogs, which have been heated by running, pant with opened
mouths and outstretched tongues, the vapor steaming forth from their
gaping throats. Dogs cool themselves in this way because they have very
little perspiration passing through their skins. Their perspiration is
really from their throats, rather than from their skins. Human beings
sometimes lose, in hot weather, as much as five pints of water in
twenty-four hours, by exhalation through the lungs and skin.
Give me now, good reader, your close attention for just a few minutes
while I return to the notion with which we started on beginning the
consideration of this subject, so that I may fit it into its right
place, and leave it well packed away with the other notions that we
have gained, while studying the value and uses of air, water, and
food. Your body is a living laboratory, formed of an enormous quantity
of little chambers and vessels. From a strong central force-pump,
placed in the middle of that laboratory, liquefied food, or blood, is
streamed out through branching supply-pipes to the several chambers,
to carry to them the materials that have to be operated upon in their
cavities for the production of animal power and warmth. The force-pump
acts by repeated short strokes, but the liquefied food flows through
chambers of the laboratory in continuous, even currents, because
the supply-pipes are made of yielding and elastic substance, like
India-rubber, and not of hard, stiff substance, like metal or wood. As
the liquefied food gushes out from the force-pump, the elastic walls
of the supply-pipes are stretched by the gush, but directly afterwards
they shrink back again, as India-rubber would do, shut close a valve
that prevents all return of the liquid into the force-pump, and so
compel the liquid to run onwards in the other direction, through the
pipes. Before the shrinking in of the pipes has altogether ended, the
force-pump renews its stroke, and so the onward flow of the liquid
never stays, although the pump has to make beat after beat. The
liquefied food gushes out from the force-pump with a speed of about
a foot in each second; but it has to supply such an enormous host of
small chambers in the remote parts of the laboratory, that it does not
flow through them with a speed greater than an inch in a minute. This,
however, is no disadvantage, as it affords plenty of time for the full
carrying out of all the intended changes in those chambers, whereby
animal power and warmth are to be produced.
Remember, then, that as your heart beats in your chest, second after
second, the red blood flushes through every crevice and every fibre
of your living frame, just as it does through your cheek when it is
crimsoned with a blush. Seventy or eighty times every minute, your
beating heart pumps, and constantly, so long as you are alive, the
flushing blood streams on everywhere. The blood, however, streams
on in this continuous way, because its flow is not stopped, even
when it has reached the remotest chambers and fibers. The trunks of
the supply-pipes divide into branching twigs, which get very fine
indeed where they are in connection with the working chambers of the
laboratory, and which then lead on into return-pipes, that are gathered
together into enlarging trunks, These, in their turn, are collected
into main tubes which end in the cavity of the heart. At the extremity
of these main trunks of the return-pipes, valves are so placed as to
prevent the pumping action of the heart from forcing the blood back
into them. Thus, as your heart pumps, swelling out and drawing in its
walls, the blood flows into its cavity by the return-pipes, and is
squeezed out therefrom through the supply-pipes. It always streams in
one direction. It circulates through the living frame which it flushes;
that is, it goes in an endless circle, now through the heart, now
through the supply-pipes, now through the return-pipes, and now starts
once again through the heart.
But as your blood thus circulates, through your living frame, fresh
nourishment, newly dissolved food, is added in some places to its
streams; in other places nourishment and fuel are taken from it to
furnish the active chambers of the laboratory with warmth and power; in
other places worn-out substance is added to it to be carried away in
its current; and at other places this worn-out substance is poured away
from it through the outlets provided for its removal. The principal
outlets through which the waste of your living laboratory is poured
away, have been already spoken of in detail—they are the pores of the
skin, the drains of the laboratory; and the pores of the lungs, that
with the mouth form the chimney of the laboratory through which the
smoke and the vapors from the burned fuel fly away. In addition to
these outlets, there is, however, another series by which some denser
matters, which can not be got through either the skin-pores or the
lungs, are streamed away. This series is continually in operation,
but the details of its arrangements are so ingeniously planned, that
it accommodates its work to the demand of each passing instant. When,
for instance, the perspiring pores of the skin are widely open for the
cooling of the frame, and an increased amount of liquid is consequently
steamed away through them, then these outlets are narrowed; but when,
on the other hand, the skin-pores are closed, or when any extra flood
of liquid is thrown into the interior of the frame during cold weather,
then the additional outlets at once are brought into very active play.
Now, just imagine the case of a large town, in which there is a certain
quantity of waste liquid needing to be carried away through drain-pipes
every day, but in which also there occur occasional excessive floods
of rain, which must have a way of escape provided for them whenever
they happen. How clever you would think it if some skillful engineer
fixed valves in the drain-pipes of that town, which kept themselves
fast closed under ordinary circumstances, but which opened of their own
accord whenever the pressure of an extra flood came, and so allowed
the excess of liquid to flow safely and freely away. Such has really
been the proceeding of the skillful Engineer of your living frame.
Your body is exposed to the risk of occasional excessive floods. When
the weather is very cold, for instance, the pores of your skin are
closed, and not more than a single pint of liquid can force its way out
through them, in the place of the four pints which would pass in warm
weather. Much of the water which would otherwise have escaped from the
channels of the supply-pipes, then remains in them, coursing round in
the progress of the circulation. Sometimes, too, in all probability
you will be tempted to swallow an unreasonable quantity of liquid,
beyond any demand the mere process of cooling an over-heated frame can
require. But whenever you have thus set up an unusual internal flood,
sluice-gates are opened, and through these the excess is rapidly poured
until the flood is got rid of. In those parts of your body which have
been named the kidneys, there are pores through which waste liquid is
always draining, without being turned into vapor or steam; but in the
kidneys there are also chambers composed of very fine walls, which
are strong enough to prevent fluid from passing through them when it
is only pressed by a gentle force, but which are not strong enough
to do so when the pressure becomes greater in consequence of the
over-flooding of the supply-pipes. The kidneys are the sluice-gates of
your body, provided with outlets for common use, and with self-acting
valves which come into operation upon occasions of excessive flood.
Thus astonishing, then, is the care which has been taken in perfecting
the arrangements of the heating service of that complicated laboratory,
your living body. Fuel is thrown into an internal furnace, more or
less plentifully, according to need. The fuel is there burned, and
fanned by air-blasts, which are strengthened or weakened as the
occasion may require. The heat produced by the burning is economized by
external packings and wrappings, or it is scattered by the opening of
evaporating pores on the external surface, and by the drenching of that
surface with steaming moisture; and self-acting valves are provided to
regulate the quantity of liquid contained in the supply-pipes, so that
the cooling pores may never be forced into mischievous activity by the
mere pressure of excess in their channels, at a time when the body is
already sufficiently chill.
When cold is suddenly applied to the previously warm skin of the
living body, it shuts up all the perspiring pores at once, and then
empties its supply-pipes of their streaming blood inwards. You know how
pale and numb your skin becomes on a cold frosty day, when you stand
quietly in the chilling air. That is because the cold squeezes all the
blood out of the small vessels of your skin. But where do you suppose
the squeezed-out blood goes to? It flows directly into the several
internal parts, choking up and overloading their channels. If the skin
be soon made warm again, the overloaded parts of the inside once more
get emptied, and recover their usual freedom; but if it be kept cold,
then their overloading and choking continues, and great discomfort is
experienced. All kinds of inflammations and disorders are produced in
this way. What are commonly known as colds are internal obstructions
of this nature. Cold in the head is an affection in which the lining
of the nostrils is overcharged with stagnating blood. Sore throat is
caused by a similar condition in the lining of the throat. And cough by
the same state in the lining of the vessels and cavities of the chest.
The mere application of a chill temperature to the skin is not alone,
however, enough to give a cold. This result chiefly comes when the
application has been made while the body is in a weakened or exhausted
state, and therefore has not the power to resist and overcome the
internal disturbance of the even blood-flow. Colds are nearly always
caught in consequence of a sudden exposure of the body to a chill,
either when it is in a state of exhaustion and fatigue from sustained
exertion, or when it has been for some time previously over-heated.
Excess of heat itself soon produces exhaustion, and depression of the
strength and the powers of life. When a chill is applied to the skin
while the body is fresh and strong, as, for instance, when a man pours
cold water over himself the instant he gets out of a warm bed in the
morning, after a sound and refreshing sleep, it does no harm, for this
reason: First, the blood is driven away from the supply-pipes of the
skin by the cold, and flows inwards; but the refreshed heart, then
becoming sensible of its arrival, rouses itself to increased effort,
and prevents obstruction by pumping on the liquid more vigorously.
By this means blood is soon sent back again to the skin in great
abundance, and makes it glow with renewed warmth. It is only when the
cold is very severe, or very long continued, that this re-action, as it
is called, would be hindered, and internal disorder be likely to be set
up.
Here, then, is one of the advantages of employing warm clothing. It
prevents the catching of cold by protecting the skin from sudden chills
at a time when the internal parts of the frame are depressed and unable
to meet, without injury, the effects which follow upon it. If at any
time you are very weary, and very warm, remember, then, that you must
keep yourself warm by drawing more clothes round you, or by some other
plan. Want of attention to this very simple proceeding, or absolute
ignorance that it ought to be adopted, is among the common means
whereby men lay up for themselves disease and suffering, and cause
sickness to take the place of health.
How constantly it happens, at the very first appearance of fine
weather in spring, that sore throats and coughs and colds are met with
everywhere. This is nearly always because people are then tempted to
throw aside the warm clothing which they have used through the winter,
and so to leave their skins very much more exposed to the influences
of the sudden chills, which are quite sure to occur at this time. Just
observe what nature herself does in this matter. She does not take off
the horse’s warm coat the moment the spring sunshine bursts out in
the sky. She compels him to keep it upon his back, at the risk of his
being a good deal encumbered by it now and then, because it is better
he should submit to this small inconvenience for a time, rather than
be exposed to the danger of a grave disease. As you may advantageously
take a lesson from the bee as to the management of fresh air in your
dwellings, so you may advantageously go to the quadruped to learn how
to manage the alteration of your clothing at the change of the seasons.
When you see the horse putting on his fine silken garment for summer,
follow his example; but until you do see this, be wise, and still keep
within the protection of your winter wools and furs.
There is another plan by which people every day expose themselves to
the danger of catching cold, and of so falling into disease. They
commonly sit in very draughty rooms; apartments which are warmed by
bright fires, but which are at the same time chilled by cold wind
rushing in at large crannies and crevices, far beyond the quantity
which is needed for the mere supply of pure air. Such rooms are warm
and cold climates brought together in a nutshell. There is a scorching
summer near the fire, and a freezing winter near the window at the same
instant. Merely walking about the room therefore takes the body in a
moment from one climate to another, and this must happen sometimes
when the body is not prepared to meet, and accommodate itself to, the
change. A chilled surface, and internal obstructions result, and colds
and diseases follow very soon. The inside of rooms should be in winter
time very much what they are in the summer season; that is, not too
hot, but equally warm in all parts, and with a sufficient current of
air passing through them to keep them pure, although not with enough to
set up dangerous draughts. If there are draughts, then the protection
of warm clothing must be constantly employed, to prevent the chilling
influence from attacking the skin. Warm and undraughty dwelling-rooms
are the natural allies of warm clothes in health-preserving power.
There is another very excellent companion and helper of warm clothes in
this good work. This helper is “exercise.” If, when you are weary and
warm, and have no additional clothes to draw round you on the instant
to prevent a chill, you sit down or stand still in the cold wind,
you will be nearly sure to catch cold, and to be made ill. But if,
on the other hand, you keep moving about until you can either clothe
yourself more warmly, or go into a warm room, then you will be almost
as certain to escape without harm. Exercise aids the heart in keeping
the blood moving briskly, and if at any time there is an inclination
for the blood-flow to stagnate and get obstructed internally, then
exercise overcomes the obstruction, and sends the lagging blood
cheerily on toward all parts of the frame, and back toward the skin.
Brisk exercise thus possesses the power to overcome mischief, as well
as to prevent it. Its influence in quickening and sustaining the flow
of the blood-streams through the supply-pipes of the body, necessarily
leads in the end to the strengthening of every structure in the frame,
and to the rousing of every operation that is carried on in the living
laboratory. Every one who values the blessing of health and strength
will do well, if his daily task is not one of exertion in the open
air, to make such a task for himself. One hour at least out of the
twenty-four should be spent in quickening the blood-streams, and in
deepening the breathing by walking briskly in some open space where the
fresh winds of heaven have free play.
But we will now imagine that in ignorance of all these particulars, or
in consequence of some long-continued exertion and exposure which the
demands of duty made it altogether impossible for you to avoid, you
have caught a cold, and are beginning to suffer from a sore throat, or
a cough, or some other sign that matters within are not as they should
be. What, under such circumstances, ought you to do to stop the cold,
and get rid of it, before serious disorder is brought about? Here,
again, warm clothing is of the highest value. If the chilled surface
be at once closely covered up, and be kept covered, the blood is soon
drawn back to the skin, and the internal obstructions are in this way
overcome. The best possible way to get rid of a cold quickly, for those
who can follow it, is to go to bed as soon as it begins, and to keep
there until the cold is cured. If you can not follow this plan, then
_drink as little of any fluid as you can_ for four or five days, and
there will soon be not enough blood, as regards quantity, in your body,
to keep internal parts overcharged, and they will be relieved, and you
will get well. There is this evil in the first plan of curing a cold:
people who have lain in bed for some time, come out of it with the
pores of their skins more than usually opened, and more than usually
disposed to suffer from any fresh chill. People who pursue the second
plan may be exposed in any way without meeting this risk.
There are thus, then, golden rules for the management of the clothing,
as well as for the management of the feeding, which all people should
have stamped on their understandings, and engraved upon their memories.
These are:
Follow the example which nature sets, and wear thicker clothing in cold
weather than in warm.
Do not lay aside the warm clothing of winter, as soon as fine, mild
weather seems to have begun, but wait until you see that nature is
taking their winter garments away from the birds and the beasts.
Never expose yourself to a chill without extra clothing, when you are
weary, as well as warm.
Never sit in draughts of cold air without putting on extra clothing.
Keep in brisk exercise when you are unable to avoid currents of chill
air, and are at the same time fatigued by exertion, and thinly clad.
Never remain in damp clothes longer than you can help. Damp clothes
chill the surface of the body very rapidly by carrying away its heat as
the moisture is turned into steam. Wet stockings, and boots, or shoes,
are injurious, for the same reason as other kinds of wet clothing. They
are not more dangerous than other kinds of damp garments, but they
have to be encountered much more frequently on account of the ground
often remaining wet for long periods, when there is no great excess of
moisture in the air. Wet feet produce harm more frequently than wet
clothes, because they are much more common.
By a careful and constant attendance to the principles laid down in
these golden rules, the attacks of many grave diseases may be avoided,
and the advantage which is intended to result from the influence of
warm clothes may be most certainly secured.