The second element is the effect on the process of oxidation of blood
under the influence of cold. We all are aware that if a portion of
dead animal or vegetable matter be placed at a low temperature, it
keeps for a considerable time; and we have evidence of dead animals
which, clothed in thick ribbed ice, have been retained from
putrefaction for centuries. Hence we say that cold is an antiseptic as
alcohol is, and chloroform, and ammonia, and other similar bodies.
Cold is an antiseptic then, but why? Because it prevents, even in the
presence of a ferment, the union of oxygen gas with combustible
matter. The molecules of oxygen, in order that they shall combine, and
in their combination evolve heat, require to be distributed, and to be
distributed by the form of motion known as heat; deprive them of this
activity, and they come into communion with themselves, are attracted
to each other, and lose to the extent of this attraction their power
of combining with the molecules of other bodies for which they have an
affinity. In an analogous, but more obvious way, we may see the same
effect of motion in the microscopic examination of blood. In the
blood, while it is circulating briskly in its vessels, there are
distributed through it, without contact with each other, the millions
of oxygen carriers called blood corpuscles. In the circulation in the
free channels of the body, the arteries and veins, it is motion that
keeps these corpuscles apart; we draw a drop of blood and let it come
to rest on the microscope glass, and as the motion ceases the
separated corpuscles run together, and adhere so firmly that we cannot
easily separate them without their disintegration. If we were able to
drive them in this state round the body, through the vessels, they
would not combine readily with the tissues; they have, in fact,
forfeited the condition necessary for such combination. So with the
oxygen they carry; when its invisible molecules are deprived of the
force called heat, which is motion, they do not readily combine with
new matter. But perfect combination of oxygen and carbon in the blood
is essential to every act of life. In the constant clash of molecule
of oxygen with molecule of carbon in the blood lies the mainspring of
all animal motion; the motion of the heart itself is secondary to
that. Destroy that union, however slightly, and the balance is lost,
and the animal body is, in a plain word, _ill_.
Cold or decreased temperature, below a given standard, which for sake
of comparison we may take at a mean of 40° Fahr., reduces this
combination of oxygen and carbon in blood. In my Lettsomian lectures
to the Medical Society of London, delivered in 1860, I entered very
fully into this subject, and illustrated points of it largely by
experiment. Since then I have done more, and although I have not time
here to state the details of these researches, I will epitomize the
principal facts. I found then that, by exposing blood in chambers into
which air can pass in and out, the blood could be oxidized at
temperatures of 70° if the distribution of air and blood were
effectually secured, and I also found a proper standard of oxidation
from a proper temperature. Afterward I proceeded to test for
combination at lower temperatures, and discovered a gradually
decreasing scale until I arrived at 40° Fahr., when efficient
combination ceased. Of course, my method was a very crude imitation of
nature, but it was sufficient to show this fair and reliable result,
that the oxidation of blood decreases as the temperature of the oxygen
decreases.
From this point I went to animal life itself. I exposed animals to
pure cold oxygen and to cold atmospheric air, and compared the results
with other experiments in which animals of similar weight were exposed
to warm air and warm oxygen. The facts gleaned were most important,
for they proved conclusively that the products of combustion, that is
to say, the products resulting from the union of oxygen and carbon,
were reduced in proportion as the temperature of the oxygen was
reduced. In the course of this inquiry another singular and
instructive fact was elicited. It has been long known that at ordinary
temperature, say 60°, pure neutral oxygen does not support animal life
so well as oxygen that is diluted with nitrogen. In the nitrogen the
molecules of oxygen are more freely distributed under the influence of
motion, that is the meaning of the observed fact. What, then, would be
the respective influence of low and high temperatures on the
respiration of pure oxygen? To settle this question, animals of the
same size and weight were placed in equal measures of oxygen gas and
common air at a temperature of 30° Fahr., and with the inevitable
result that the animal in the pure oxygen ceased to respire one-third
sooner than did the animal in common air. Carrying the inquiry
further, I found that if the oxygen gas were warmed to 50° Fahr., the
respiration was continued six times as long as in the previous
experiment, while if the warming were carried to 70°, it was sustained
twenty-four times as long. I reversed the experiment; I made oxygen
with cold produce anæsthetic sleep in a warm-blooded animal.
I need not carry this argument further; it is the easiest of the
demonstrative facts of physiological science that reduction of
temperature lessens the combining power of oxygen for blood, and
therewith causes a reduction of animal force, and a tendency to arrest
of that force, which, in the end, means _death_.