168 PRACTICAL PHYSIOLOGY 



CHAPTER XXXIV 

 ANIMAL HEAT 



Difference between Warm-blooded and Cold-blooded Animals. 



Warm-blooded animals, such as mammals and birds, regulate their 

 bodily heat so that their internal temperature remains constant 

 notwithstanding changes in the temperature of their environment ; 

 there is little or no difference in the internal temperature of men 

 whether they be living in the tropics or in the arctic regions. Cold- 

 blooded animals cannot regulate their bodily heat ; their internal 

 temperature varies with and in the same direction as that of their 

 surroundings. There is, however, no hard and fast distinction 

 between the warm-blooded and the cold-blooded animals. Hiber- 

 nating mammals, such as the hedgehog, dormouse, and bat, are 

 warm-blooded during the time of activity, but become cold-blooded 

 when they hibernate. Young mammals and birds in a natural 

 condition of immaturity, when they are naked and blind, cannot 

 maintain their temperature at a constant level ; they need the 

 warmth of the parent's body. A similar condition is seen in 

 delicate or premature infants. 



The Temperature of Man. The average temperature of man is 

 984 F. (36-89 C.). It is taken by means of a clinical thermometer 

 which is either inserted in the rectum, axilla, or mouth, or the 

 subject micturates over the bulb of the thermometer. Take the 

 temperature of your body at each hour of the day. Chart out 

 the results on a temperature chart and observe the daily variation 

 (Fig. 160). Take the temperature before and immediately after 

 muscular exercise, such as a fifteen minutes' run. The temperature 

 may rise to 100-101 F. (37-78-38-33 C.) or even more on a hot 

 day. A rise of temperature can be constantly observed if the 

 thermometer be placed in the rectum or stream of urine ; the 

 buccal temperature may for the reasons given below show a fall in 

 temperature during muscular work. It is important to remember 

 that the daily range in the internal temperature of a healthy man 

 may be from 97-0 F. (36-1 C.) to 99-6 F. (37-56 C.) ; and that 

 observations taken in the mouth, even when it is firmly closed, are 

 liable to be low, owing to the danger of cooling of the tissues of 

 the mouth, externally by cold air, internally by the inspired air. 



Heat Regulation. Take a large frog, and insert a small ther- 

 mometer in the rectum or flex up the thigh, and insert the ther- 

 mometer between it and the abdomen, and record its temperature. 

 Place the frog in warm water at 30 C. After ten minutes observe 

 its temperature. It will have reached the same temperature as 

 the water. Cool the frog again in cold water and take its tempera- 

 ture again. Then place it for ten minutes in a thermostat heated 

 to 35 C. In the dry warm air the frog's temperature will not 



