Without entering on the question whether heat is the animating
principle of all living organisms, we may accept that in the evolution
of heat in the body we have a measurement of the capacity of the body
to sustain motion, which is only another phrase for expressing the
resistance of the body to death. For example, if we assume that a
healthy man of thirty respires sufficient air per day to produce as
much heat as would raise fifty pounds of water at 32° Fahr. to 212°
Fahr., and if we assume that a man of sixty in the same temperature is
only able to respire so much air as shall cause him to evolve so much
heat as would raise forty pounds of water from 32° to 212°, we see a
general reason why the older man should feel an effect from a sudden
change in the temperature of the air which the younger would not feel;
and if we assume, further, that a man of eighty could in the same time
produce as much heat as would raise only twenty pounds of water from
32° to 212°, we see a good reason why the oldest should suffer more
from a decrease of external temperature than the other two. It is
necessary, however, to know more than this general statement of an
approximate fact; we ought to understand the method by which the
reduction of temperature influences, and the details of the
physiological process connected with the phenomena. When a human body
is living after the age when the period of its growth is completed and
before the period of its decay has commenced, it produces, when it is
quite healthy, by its own chemical processes, so much heat or force as
shall enable it, within given bounds, (1) to move its own machinery;
(2) to call forth, at will, a limited measure of extra force which has
been lying latent in its organism; and (3) to supply a fluctuating
loss that must be conveyed away by contact with the surrounding air,
by the earth, and by other bodies that it may touch, and which are
colder than itself. There is thus produced in the body, _applied_
force, _reserve_ force, and _waste_ force, and these distributions of
the whole force generated, when correctly applied, maintain the
perfect organism in such balance that life is true and steady. So much
active force carries with it the power to perform so much labor; so
much reserve force carries with it the power to perform a measure of
new or extra labor to meet emergencies; so much waste force enables
the body to resist the external vicissitudes without trenching on the
supply that is always wanted to keep the heart pulsating, the chest
breathing, the glands secreting or excreting, the digestive apparatus
moving, and the brain thinking or absorbing.
Let us, even in the prime of manhood, disturb the distribution of
force ever so little, and straightway our life, which is the resultant
of force, is disturbed. If we use the active force too long, we become
exhausted, and call on the reserve; if we continue the process, the
result is failure more or less perfect, sleep, and, in the end, the
last long sleep. Let us, instead of exhausting the force, cut it off
at the sources where it is generated; let us remove the carbon or coal
that should go in as fuel food, and we create prostration, and in
continuance a waning animal fire, sleep, and death; or let us, instead
of removing or withdrawing the supply of fuel, cut off the supply of
air, as by immersion of the body in water, or by making it breathe a
vapor that weakens the combination of oxygen with carbon--such a vapor
as chloroform--and again we produce, at once, prostration, sleep, or
death, according to the extent to which we have conducted the process.
Lastly, if instead of using up unduly the active and reserve force, or
of suppressing the evolution of force by the withdrawal of its
sources, we expose the body to such an external temperature that it is
robbed of its heat faster than it can generate it; if to supply the
waste heat we draw upon the active and reserve forces, we call forth
immediately the same condition as would follow extreme over-exertion,
or suppression of the development of force; we call forth exhaustion
and sleep, and, if we go far enough, death.
We have had in view, in the above description, a man in the prime of
life, in the center of growth, and decay. In regard to the force of
animation in him, let us look at him now retrospectively and
prospectively. In the past his has been a growing, developing body,
and in the course of development he has produced an excess of force
commensurate with the demands of his growth; this has enabled him
gradually to bear more fatigue and more exposure, without exhaustion,
and even with ease, until he has reached his maximum. When he has
stopped in development, when he stands on a fair level with the
external forces that are opposed to him, then his own force, for a
short time balanced, soon stands second in command. He feels cold more
tenderly; if his rest be broken, the demand for artificial heat is
more urgent; if he lose or miss food, he sinks quickly; and, returning
to our facts, as to the influence of the external temperature on
mortality, these are the reasons why a fall in the thermometer sweeps
away our population according to age so ruthlessly and decisively.
If we analyze the facts further by the side of the diseases which kill
the old, we find those diseases to be numerous in name, but all of two
types. They are diseases which of themselves tend either to produce
undue loss of force, or that tend to prevent the development of force
at its origin. Thus affections which are accompanied with exhaustive
loss of fluids from the body, such as diabetes, dropsies, and
hæmorrhages, are of the first class; affections in which due supply of
air to the lungs is prevented are of the second class, especially
bronchitis, a disease so commonly assigned as the cause of the deaths
among the members of the aged and enfeebled population, that succeed
immediately on an extreme fall of the thermometer.