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 birth.  Kittens, rabbits and puppies, if removed from their surroundings shortly after birth, lose their body heat until their temperature has fallen to within a few degrees of that of the surrounding air.  But such animals are at birth blind, helpless and in some cases naked.  Animals who are born when in a condition of greater development can maintain their temperature fairly constant.  In strong, healthy infants a day or two old the temperature rises slightly, but in that of weakly, ill-developed children it either remains stationary or falls.  The cause of the variable temperature in infants and young immature animals is the imperfect development of the nervous regulating mechanism.