92 PRACTICAL PHYSIOLOGY 



CHAPTER XXII. 

 BODY HEAT AND SECRETION OF SWEAT. 



The Normal Temperature. 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 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. 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'l 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 cloaca or flex up the thigh, and insert the thermometer 

 between it and the abdomen, and record its temperature. Place the frog 

 in warm water at 30 C. After 10 minutes observe its temperature. 

 It will have reached the same temperature as the water. Cool 

 the frog again in cold water and take its temperature again. 

 Then place it for 10 minutes in a thermostat heated to 35 C. In 

 the dry warm air the frog's temperature will not rise to more than 

 about 30-33 C. This is owing to the evaporation of water from the 

 frog's skin. Take the temperature of a small mammal in the rectum 

 and then place it in the thermostat at 30 C. for 10 minutes. The 

 temperature of the animal will scarcely vary. Note the quickened 

 respiration of the animal. This increases the evaporation of water 

 from the lungs. Note the way it sprawls out its limbs so as to increase 

 the loss of heat by radiation, convection, and conduction. A man 

 cannot bear for more than a few minutes immersion in a bath of 

 water at a temperature of 44 C., but he can stay for twenty minutes 

 in a dry atmosphere heated to 121 C. The body temperature is 

 then regulated by sweating. It takes 5'55 Cal. 1 to evaporate 1 gram of 



1 A calorie is the heat required to raise 1 g. water 1 C. A large Calorie spelt 

 with a capital C is the heat required to raise 1000 g. water 1 C. 



