HYGIENE OF ANIMAL HEAT.
571. The amount of heat generated in man and inferior animals depends
upon the quantity and quality of the food, age, exercise, the amount
and character of the respired air, condition of the brain, skin, and
general system.
572. _Animal heat is modified by the proportion of digestible carbon
which the food contains, and by the quantity consumed._ As the kind of
fuel that contains the greatest amount of combustible material evolves
the most caloric when burned, so those articles of food that contain
the greatest quantity of carbon produce the most heat when converted
into blood. The inhabitants of the frigid zones, and individuals in
temperate climates during the cold season, consume with impunity
stimulating animal food, that contains a large proportion of carbon,
while the inhabitants of the tropical regions, and persons in
temperate climates during the warm season, are more healthy with a
less stimulating or vegetable diet.
_Observation._ When we ride or labor in cold weather, an adequate
amount of nutritious food will sustain the warmth of the system better
than intoxicating drinks.
573. _Age is another influence that modifies the generation of animal
heat._ The vital forces of the child being feeble, less heat is
generated in its system than in that of an adult. The experiments
of Dr. Milne Edwards show that the power of producing heat in
warm-blooded animals, is at its minimum at birth, and increases
successively to adult age; and that young children part with their
heat more readily than adults, and, instead of being warmer, are
generally a degree or two colder. After adult age, as the vital powers
decline, the generation of heat is diminished, as the energies of
the system are lessened. Hence the young child, and the debilitated
aged person, need more clothing than the vigorous individual of
middle age.
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571-585. _Give the hygiene of animal heat._ 571. State some of the
influences that modify the generation of animal heat. 572. What
element of the food influences the generation of heat? When and
where can animal food be eaten with impunity? Give the practical
observation.
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574. _Exercise is an influence that modifies the generation of animal
heat._ As carbon and hydrogen enter into the composition of the organs
of the body, whatever increases the flow of blood in the system,
increases also the deposition of new material, and the removal of the
waste particles. This change among the particles of matter is attended
with an elevation of temperature, from the union of oxygen with the
carbon and hydrogen of the waste atoms. For this reason, a person in
action is warmer than in a quiescent state. Consequently, the amount
of clothing should be increased, when exercise or labor is diminished
or suspended.
575. On the other hand, whatever impedes the circulation and the
interchange of the atoms of matter, diminishes animal heat. Common
observation shows, that the extremities are not as warm when tight
gloves or boots are worn as when they are loose. One reason is, the
circulation of blood is impeded, which is attended with less frequent
change of the particles of matter.
576. _The quantity of air which is inhaled modifies the heat of the
system._ In the generation of heat in a stove, air, or oxygen, is as
essential as the wood or coal. It is equally so in the production of
animal heat. The oxygen of the inspired air should be in proportion to
the carbon and hydrogen to be consumed. This requires voluminous
lungs, together with free movements of the ribs and diaphragm. A
person whose chest is small, and whose apparel is worn tight over the
ribs, suffers more from the cold, and complains more frequently of
chilliness and cold extremities, than the broad-chested and loosely
dressed.
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What do the experiments of Dr. Milne Edwards show? 574. Why does
exercise influence animal heat? 575. What is the effect when the
circulation of blood is impeded? Give examples. 576. Why do those
persons that have broad chests and voluminous lungs suffer less from
cold than the narrow-chested with small lungs?
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_Observation._ Fishes that breathe by means of gills, as the cod,
pike, &c., depend solely on the small quantity of oxygen that is
contained in the air mixed with the water. Their temperature is not
much greater than the medium in which they live. Whales, dolphins,
&c., breathe by means of lungs, and the inhalation of atmospheric air
makes their temperature about 100 deg., independent of the heat of the
element in which they live.
577. _The quality of respired air influences the generation of animal
heat._ In vestries, and other public rooms, when crowded with an
audience, where the ventilation is inadequate, the lamps will emit but
a faint light, because the oxygen is soon expended, and there is not
enough of the vivifying principle to unite with the oil and disengage
light. In the human body, when the respired air has lost some of its
life-giving properties, the combustion that takes place in different
parts of the system is not so complete as when it contains a proper
proportion of oxygen; and hence less heat is disengaged. For this
reason, those persons that breathe impure air, either in the daytime
or night, require more clothing, than those that work and sleep in
well-ventilated rooms.
578. _The condition of the brain and nervous system affects the
generation of animal heat._ If the brain is diseased, or the mind is
absorbed in thought, depressed by sorrow, or aroused from fear, the
breathing becomes slow and scarcely perceptible, and a chilliness
pervades the body, particularly the extremities; while, on the
contrary, if the mind and nervous system are excited by joyous and
agreeable emotions, the circulation of blood is quicker, and the
system more powerfully resists external cold. During sleep, when the
brain is partially inactive, less heat is generated than when awake.
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What is said of those fishes that breathe by means of gills? Of those
that breathe by means of lungs? 577. Why do lamps give but a faint
light in crowded, unventilated rooms? What effect on animal heat has
impure air? 578. Mention the effects of some of the mental emotions on
animal heat.
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_Observation._ The preceding remark explains why an individual who
sleeps in the same clothing that was adequate to prevent chills while
awake, contracts a cold, unless he throws over him an additional
covering.
579. _The state of the skin exercises much influence in the generation
of heat._ If the functions of this membrane are not interrupted, more
heat will be generated than when it is pallid and inactive. The action
of the capillaries is most energetic when the skin is clean; on this
account, before taking a walk or a ride, in cold weather, remove all
impurities from the skin, by thorough ablution and vigorous friction.
580. _The amount and kind of clothing modify the temperature of the
system._ Those persons that are well clothed have greater power to
resist cold than the thinly apparelled, because both the evaporation
and the radiation from the skin are impeded, and less heat, in
consequence, is abstracted from the body. If the articles of apparel
possess the property of retaining air in their meshes, as flannel, the
removal of heat is not as rapid as when linen is worn.
_Observation._ In winter, although more heat is generated in the
system than in summer, yet we require more clothing, and also those
articles that are poor conductors of heat, because caloric is more
rapidly extracted in clear, cold weather, than in a warm day.
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What does the preceding remark explain? 579. What suggestion
respecting the condition of the skin before taking a walk or ride in a
cold day? Why? 580. Do the amount and kind of clothing affect animal
heat? What is said of well-clothed persons? When does the system
generate the most heat?
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581. _The health and constitution influence the generation of heat._
When the health is firm, and the constitution vigorous, less clothing
is needed, for the change among the particles of matter is more rapid,
and more heat is generated, than when the opposite condition obtains.
Persons of a feeble constitution, particularly, if any of the vital
organs[18] are diseased, need more clothing and require rooms of a
warmer temperature, than individuals who are free from disease and
have a vigorous constitution.
[18] The brain, lungs, heart, and digestive organs, are called _vital_
organs.
_Observation._ Persons who are infirm, and whose vital powers are
feeble, in general, accustom themselves to an undue amount of clothing
and warm rooms. A more judicious practice would be, to exercise more
and use a moderate amount of clothing, together with a more nutritious
diet.
582. _The surplus heat should be removed equally from all parts of the
system._ The rapid evaporation of fluids, as in free perspiration, or
from radiation, as in a cold atmosphere, is attended with a removal of
heat from the system. This modifies the action of the circulatory
vessels. Consequently, if heat is suddenly and rapidly abstracted from
one part of the system, the equilibrium of the circulation is
destroyed, which will produce disease.
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Why do we, then, require more clothing in winter than in summer? 581.
Why do persons of firm health and vigorous constitutions need less
clothing than those who are feeble? What is a general practice among
infirm persons? What would be more judicious? 582. Why should the
surplus heat be removed equally from all parts of the system? What is
said respecting currents of air from small apertures?
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_Observation._ Currents of air that impinge upon small portions of the
body, as from small apertures, or from a window slightly raised,
should be avoided. They are more dangerous than to expose the whole
person to a brisk wind, because the current of air removes the heat
from the part exposed, which disturbs the circulation of blood and
causes disease, usually in the form of "colds." For the same reason,
it is not judicious to stand in an open door, or the opening of a
street.
583. _The system suffers less when the change of temperature is
gradual._ The change in the production of heat, as well as in the
evaporation of fluids from the system, is gradual when not influenced
by foreign causes. This gradual change is known under the name
_acclimation_. By this means the body is enabled to endure tropical
heat and polar cold. Owing to this gradual adaptation of the system to
different temperatures, we can bear a greater degree of heat in the
summer between the tropics, than in the winter under the polar
circles. On the other hand, we can endure a greater degree of cold in
winter and in the arctic region, than in the summer and in equatorial
countries.
584. The sensation of heat which would be oppressive in a mild, warm
day of January, would only be grateful in July, and a degree of cold
which could scarcely be endured in August, would not be uncomfortable
in December. The changes of season in our latitude prevent the
disagreeable and perhaps fatal consequence that would follow, if no
spring or autumn intervened between the severity of winter's cold and
the intensity of summer's heat. During the transition periods, the
constitution is gradually changed, and adapted to bear the extremes of
temperature without suffering. The amount of heat generated in the
nutrient capillary vessels, is likewise diminished or increased as the
temperature of the season becomes greater or less.
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583. In what manner should change of temperature take place, to be
adapted to the body? How is the body enabled to endure tropical heat
and polar cold? State some of the effects of the gradual adaptation of
the system to different temperatures. 584. What is said relative to a
warm day in winter? To a cold day in summer? What is said of the
changes of seasons in our latitude? What effect on the constitution
during spring and autumn? What change in the amount of heat
generated?
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585. But, on the contrary, we cannot suddenly pass from one extreme of
temperature to the other with impunity. Let an inhabitant of Quebec
suddenly arrive in Cuba in February, and he would suffer from languor
and exhaustion; after becoming acclimated to this tropical climate,
let him suddenly return to Quebec in January, and the severity of the
weather would be almost insupportable.
_Observations._ 1st. Experience shows that heated rooms, as well as
tropical climates, lessen the generation of heat in the body, and
likewise the power of resisting cold. It would be idle for the
merchant from his warehouse, or the mechanic from his heated shop, to
attempt to sit on the box with a coachman, with the same amount of
clothing as his companion, who is daily exposed to the inclemency of
the weather.
2d. "It is the power of endurance of cold at one period, and the
absence of its necessity at another, that enables animals, in
their wild and unprotected state, to bear the vicissitudes of the
seasons with so little preparation in clothing, and so little real
inconvenience."
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585. What effect on the system has a sudden transition from a cold to
a warm climate? What does experience show? Why do wild animals bear
the vicissitudes of the seasons with so little preparation in
clothing?
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