bounds of certain extremes, the temperature
of mammifers, like that of birds, varies
according to the family, the genus, or the
species to which they belong; it is found
to be not identically the same in different
individuals of the same species. The climate,
the season, the different hours of day or
night, and many other physiological
conditions, influence the general temperature of
animals, or the local temperature of diverse
parts of their bodies. The sheep, the goat,
the dog, the cat, and the rabbit, are among
the hottest of quadrupeds.

The temperature of an adult man, taken at
the armpit, which gives the heat of the
trunk, varies in the temperate zone between
thirty-six and a half degrees and thirty-seven
and a half, centigrade. The force of resistance
which the superior animals oppose to
every cause of refrigeration is sufficiently
proved by the narratives of Arctic voyagers,
who have lived in an atmosphere seventy
degrees below zero, or freezing point, without
experiencing any notable alteration of their
own temperature. Captain Parry found that
the Arctic fox was more than seventy-six
degrees warmer than the surrounding air;
and Captain Back records that a willow
grouse was more than seventy-nine degrees
hotter than the air it breathed.
Consequently, birds and mammifers may be
considered as creatures whose temperature is
physiologically a constant quantity.

Under the denomination of inferior animals,
may be comprised the two last classes of
Vertebrata, namely, reptiles and fishes, and all
the Invertebrata or backboneless creatures.
Although very differently organised, they
are brought into fellowship by the common
property that their temperature, unlike that
of mammifers and birds, does not maintain
itself sensibly fixed and independent of
external circumstances, but is subject to
considerable variations, which follow the
variations of the medium, whether air or
water, in which they live. The observation
of their vital heat presents considerable
difficulties. For creatures of very small volume,
observers have frequently employed a special
artifice, which consists in enclosing a certain
number of them in a small glass vessel, in
such a way, that they should be crowded
round the bulb of a small thermometer. This
mode has the advantage of preventing
evaporation and the cold, which is its consequence.
Newport, in his researches into the
temperature of insects, seized his subject with a
pair of pincers, and so applied and kept it in
constant contact with the bulb of his
thermometer, thereby avoiding any
communication of heat from his own hands. To avoid
radiation outwards, and evaporation, he took
the precaution of wrapping the insect and the
bulb in a piece of wool.

The temperature of reptiles has been the
subject of numerous observations. The
results obtained prove that they are all warmer
than the air or the water in which they live,
and that they by no means deserve the
reproach of being cold-blooded animals; on
the contrary, they all produce a certain
quantity of heat which is appreciable by scientific
instruments, although very inferior to that of
birds and of quadrupeds proper. The lizards
are generally the warmest; then the vipers,
adders, and snakes; then the tortoises;
while frogs and toads appear to be endowed
with a much feebler power of generating
heat. But, generally speaking, the proper
temperature of reptiles is very variable.

The same remarks apply to fish. The
ravenous pike seems to be one of the hottest-
tempered fellows of his class; and, what we
should hardly expect to find, those nimble
gambollers, the bleak, the trout, and the
flying-fish, are chilly to, not a degree, but to
half a degree and less above the chilliness of
the water which bathes their agile bodies.
The shark is not much more warmly constituted.
The eel, also, is of a cool temperament;
but what is most remarkable about
the eel is, that although so tenacious of life
under violence, he is extremely sensitive to
any extreme temperature, either in the
ascending or the descending scale. Still not
only is it proved that fishes have the power
of producing heat, but also that the muscular
parts of their bodies, exactly the same
as in birds and quadrupeds, are decidedly
warmer than the other portions of their frame.

Swammerdam, without giving any
thermometric degree, states that, even in the
depth of winter, the temperature of beehives
is considerably above that of the atmosphere.
Réaumur and Huber have confirmed the
fact. Newport, observing a hive under the
same circumstances, caused its temperature
to rise to a high degree, by awaking and
exciting the bees. Similar phenomena have
been produced in the nests of wasps and ants.
Nobili and Melloni endeavoured to ascertain
the proper temperature of insects by means
of an ingenious thermo-electrical apparatus;
and they state that after operating on more
than forty indigenous species in the various
stages of metamorphosis assumed by those
creatures, every indication of the needle was
positive, that is, indicative of the creature's
superior warmth, without a single exception.
Newport has proved that the proper
temperature is highest in insects which fly (and
amongst them in bees and sphynxes) than in
all the other articulated animals. Experiments
made on molluscs also establish their
faculty of producing heat. Snails and slugs
maintain a degree of warmth sensibly superior
to that of the ambient medium. So do
cuttle-fish, sea-urchins, and sea-anemones.
Star-fish and all zoophytes follow exactly the
same rule. Valentin discovered that amongst
the inferior creatures the proper temperature
of the crustaceans is the highest, and that
of the polypes the lowest; and that their
power of producing heat increases exactly in