in rabbits suffering from
rabies during the last period of their life, the rectal temperature
being then within a few degrees of the room temperature and varying
with it. He explains this condition by the assumption that the nervous
mechanism of heat regulation has become paralysed. The respiration and
heart-rate being also retarded during this period, the resemblance
to the condition of hibernation is considerable. Again, Sutherland
Simpson has shown that during deep anaesthesia a warm-blooded animal
tends to take the same temperature as that of its environment. He
demonstrated that when a monkey is kept deeply anaesthetized with
ether and is placed in a cold chamber, its temperature gradually
falls, and that when it has reached a sufficiently low point (about
25 deg. C. in the monkey), the employment of an anaesthetic is no longer
necessary, the animal then being insensible to pain and incapable of
being roused by any form of stimulus; it is, in fact, narcotized
by cold, and is in a state of what may be called "artificial
hibernation." Once again this is explained by the fact that the
heat-regulating mechanism has been interfered with. Similar results
have been obtained from experiments on cats. These facts--with
many others--tend to show that the power of maintaining a constant
temperature has been a gradual development, as Darwin's theory of
evolution suggests, and that anything that interferes with the due
working of the higher nerve-centres puts the animal back again, for
the time being, on to a lower plane of evolution.

[Illustration: Chart showing diurnal variation in body temperature,
ranging from about 37.5 deg. C. from 10 A.M. to 6 P.M., and falling to
about 36.3 deg. C. from 2 A.M to 6 A.M.]

_Variations in the Temperature of Man and some other Animals_.--As
stated above, the temperature of warm-blooded animals is maintained
with but slight variation. In health under normal conditions the
temperature of man varies between 36 deg. C. and 38 deg. C., or if the
thermometer be placed in the axilla, between 36.25 deg. C. and 37.5 deg. C.
In the mouth the reading would be from .25 deg. C. to 1.5 deg. C. higher than
this; and in the rectum some .9 deg. C. higher still. The temperature of
infants and young children has a much greater range than this, and is
susceptible of wide divergencies from comparatively slight causes.

Of the lower warm-blooded animals, there are some that appear to be
cold-blooded at b