REGULATION OF TEMPERATURE. 831 



of that part above 34, whereas the temperature of the abdomen was 

 only 3 2 *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 EEGULATION 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 already 

 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. Ixv. p. 484. This article, p. 814. 



