REGULA TION OF TEMPER. I TURE. S3 1 
of that part above 34°, whereas the temperature of the abdomen was 
only 32°*5. The highest temperature observed in healthy men was 
35°"6, on the skin of the face. 
Kunkel concludes from his observations that the temperature of the 
human skin is almost constant, and that the temperature of the body is 
regulated to a very slight degree by changes in the temperature of the 
skin. 
The Regulation of Temperature. 
Inasmuch as the constancy of temperature varies in different 
animals, and even in the same animal under different conditions, such 
as age and hibernation, so also various grades of perfection are observed 
in the power of regulation. In man this power is so greatly developed 
that his temperature is almost the same, whether he lives in the Arctic 
regions, with an external temperature 50° below zero, or in the Tropics, 
where the temperature of the air may be as high as 48°. For shorter 
periods a man can remain in a room heated to 121° without the 
temperature of his body rising above the normal. 1 Other mammals 
have a less perfect regulation, as shown by the greater variations of 
their temperature. 
In young immature mammals and birds the power of regulation 
is imperfect, for when they are exposed to cold their temperature falls, 
and they pass into a condition in which they resemble the cold-blooded 
animals, their temperature rising and falling with that of their sur- 
roundings. A similar imperfection in regulation is seen in some 
mammals during hibernation. Lastly, in the so-called cold-blooded 
animals, there are various grades in this capacity for regulating tempera- 
ture, as is shown by the high temperature of bees in winter, when com- 
pared with that of most of the lower animals, in which there is a mere 
trace of regulation. 
Even in those warm-blooded animals which possess a perfect power 
of heat regulation, there are limits to this power. If the animal be 
exposed to excessive cold, the loss of heat is great, and only within 
certain limits can compensation be effected by an increased produc- 
tion of heat. When compensation fails, then the animal's temperature 
falls, its bodily and mental activities are diminished, and it passes into 
a sleepy, unconscious condition which ends in death. Such a condition 
is observed in men or animals before they are " frozen to death." 
On the other hand, extreme heat can only be resisted within a 
certain range ; the production of heat in the body can be diminished, 
but not suspended ; the loss of heat can be greatly increased by sweating 
and by a greater exposure of blood in the vessels of the skin, but if the 
air be of a temperature equal to, or nearly equal to, that of the body, 
and greatly laden with moisture, then the loss of heat is slight or even 
suspended. Under such circumstances the internal temperature of the 
animal rises rapidly to a point incompatible with life. The extremes 
of heat and cold which can be borne without injury to life, have alreadv 
been discussed. 
The mean temperature of the higher animals is fairly constant 
under very great differences of external temperature, and to maintain 
such a condition the loss and the production of heat must be almost equal, 
That there is no perfect equality has already been shown in the daily 
1 Bladgen, Phil. Trans., London, 1775, vol. lxv. p. 484. This article, p. S14. 
