ADVANCED EXPERIMENTAL PHYSIOLOGY 



169 



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 and then place it in a dry thermostat at 30 C. for 

 ten 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. 



a.m. 



p.m. 



789 10 11 12 1 2 3 456 7 8 9 10 11 12 12 3 456 7 



FIG. 160. Daily variation of temperature (urine) of man. (M.S. P.) 



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

 radiation, convection and conduction. It may be readily taken 

 by a mercurial thermometer with a flat bulb. A difference of 

 10 C. may be observed in the temperature of the skin of the hand 

 in summer and winter ; in warm weather the cutaneous blood- 

 vessels are dilated, in cold weather they are contracted. The 

 temperature, however, of those parts of the body which are con- 

 stantly covered with clothing shows little change. 



Clothes diminish the loss of heat from the body by enclosing 

 layers of stationary air, so that the surface of the trunk and 

 limbs is surrounded by a layer of air nearly as warm as the 

 skin. 



EXPERIMENT. Take the temperature of the skin of the hand and 

 compare it with that of the chest or abdomen. Compare also the 

 temperatures recorded in the air space between the coat and waist- 



