200 PEACTICAL PHYSIOLOGY 



high up in the neck, and even if the nerves be cut below the laryngeal 

 branches, the paralysis of the oesophagus leads to such an accumulation 

 of food therein that particles pass over into the respiratory tract. Dogs 

 with a double oesophageal fistula have lived for months after section 

 of both vagi ; the fistulae prevent the passage of food or saliva into the 

 trachea and lungs. 



CHAPTER LVI. 

 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 not- 

 withstanding 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. Hibernating 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 con- 

 dition is seen in delicate or premature infants. 



The Temperature of Man. The average temperature of man is 

 98*4 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 mouth at each hour of the day. Chart out the results on a 

 temperature chart and observe the daily variation (Fig. 192). Take 

 the temperature before and immediately after muscular exercise, such 

 as a fifteen minutes' run. The temperature may rise to 100-101F. 

 (37 -7 8-38 -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 impor- 

 tant to remember that the daily range in the internal temperature of a 

 healthy man may be from 97-0 F. (36-l C.) to 99-6 F. (37'56 C.) ; 



