to the general laws of interchange of
temperature with neighbouring bodies, (whether
through contact or by means of conducted
heat, or at a distance, in consequence of the
radiation of heat); nevertheless, as long as
life remains, whatever place they may occupy
in the scale of being, they enjoy the remarkable
faculty of not necessarily assuming an
equilibrium of temperature either with the
inorganic bodies or other living organisms
which are placed in their immediate
neighbourhood, nor with the gaseous or liquid
medium in which they may be completely
enveloped. Thus, a living cormorant—
whether it is reposing on the surface of a
rock, or has hidden itself up to the tip of its
bill in a tangled bed of water-weeds, or is
taking a lofty flight through the clouds, or
is diving to considerable depths in search of
finny prey—does not gradually acquire the
temperature of the rock, nor that of the bed
of aquatic plants, nor that of the upper
atmosphere, nor that of the water at the
bottom of the lake. The cormorant, so long
as it is animated by the vital spark,
maintains its own proper temperature.

In the normal conditions of their development
and their existence, that is, while they
are in a healthy and natural state, organised
beings have and, what is more, preserve, a
temperature superior to that of the
surrounding medium. The most careless
observation suffices to demonstrate the fact in
respect to birds and quadrupeds. The pigeon,
the swallow, and the bat, who hover for
hours suspended in air; the dab-chick, the
otter, the penguin, the seal, and the water-
rat, who remain submerged, some for
considerable and frequent intervals, and others
for the greater portion of their time; the mole
and creatures who burrow underground,
whom we might naturally believe to be
chilled by the constant contact of the soil;
all maintain a degree of warmth perceptibly,
nay remarkably, higher than that of their
habitat. In order to verify the correctness
of the proposition with respect to the rest of
the animal kingdom, and throughout the
whole extent of the vegetable kingdom, it is
necessary to have recourse to the most
delicate methods of investigation, and, above
all, to be carefully guarded against the
refrigerating effects of evaporation; but the
fact is not the less general, and at the
present day incontestable. Both animals and
vegetables which live in air necessarily lose
at their cutaneous and respiratory surfaces
a certain quantity of water, which is
dissipated in the atmosphere under the form of
vapour. Now, this water borrows from the
living being, and carries away with it, the
entire quantity of sensible heat necessary to
maintain it at the temperature of the living
organism from which it is derived, and also
all the latent heat necessary to allow it to
pass from the state of a liquid to the state of
vapour. The double evaporation from the
lungs and the skin is, therefore, for aërial
(in contradistinction to aquatic) plants and
animals, an incessant and sometimes a very
powerful cause of refrigeration.

When, exceptionally, the surrounding
temperature rises above forty or forty-five degrees
centigrade, living beings, unlike inanimate
substances, refuse to receive the additional
heat, and maintain themselves at a temperature
lower than that which environs them.
During the great heats of an African summer,
a dead body is hotter to the touch than a
living man; and the live man continues
comparatively cool, provided the external influence
is neither long enough nor intense enough
to compromise his existence definitely.

The comparative study of the temperature
of animals and of that of the medium—air or
water—in which they live, has caused them
to be divided into two very natural groups.
The first comprises the mammifers and birds,
for whom has long and exclusively been
reserved the denomination of hot-blooded
animals, because they were wrongly
considered to be the only living creatures
endowed with a temperature of their own.
Into the second group were swept all the
other animals who are still generally
designated by the incorrect epithet of
cold-blooded. With these last, the production of
heat is sufficiently feeble to have been placed
in doubt by some physiologists. For a long
time, in fact, it was believed that their
temperature is simply that of the surrounding
medium, and that it follows its temperature
in all its variations. Numerous facts,
furnished by exacter methods of observation,
have rectified this popular error.

Of all the organised beings, birds have the
highest temperature; the common hen, the
domestic pigeon (at liberty), the guinea-fowl,
and the duck, are amongst the topmost on
the thermometric scale. The hot blood of
the pigeon doomed it to be the victim sacrificed
in many of the barbarous remedies of
olden time, such as spirting its fresh-drawn
arterial blood into a wounded human eye,
or applying the whole bird, split asunder
alive along the backbone, to the soles of the
feet, as a cure for any great defect of spirits
or decay of strength. The mammifers,
although taking higher rank in the scale of
animality, are sensibly inferior to birds in
point of temperature; nevertheless, the
difference is not so great as to prevent the
highest healthy heat of quadrupeds from
rising above the lowest healthy heat of birds.
In spite of their continued existence in the
water, the Cetaceæ, the whales and porpoises,
are no exception to the above remark; while
the case is just the contrary with hibernating
mammifers. Although their organisation
assigns them a high place in the scale of
being, these creatures, by the phenomena of
their calorification, are almost completely
associated and put on an equality with
members of the inferior classes. Within the