erable 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 deg. Fahr., reduces this
combination of oxygen and carbon in blood. In my Lettsomian lectures
to the Medical Society of London, delivered