ELEMENTARY EXPERIMENTAL PHYSIOLOGY 



201 



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 thermometer 

 in the rectum 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 tempera- 

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

 the frog again iii cold water and take its temperature again. Then 

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



F. 



7 8 9 10 11 12 1 2 3456 789 10 11 12 12 3456 7 



FIG. 192. Daily variation of temperature of man. (M. S. P.) 



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 mouse in the rectum arid then place 

 it in a dry 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. 



Loss of Heat. An approximate estimation of the amount of 

 moisture lost by a man during exercise or exposure to heat can be 

 made by weighing him naked before and after the exercise. Moisture 

 is lost from the skin and lungs, chiefly from the former. 



The temperature of the skin also influences the loss of heat by 



