ANIMAL HEAT 511 



man it has been observed that exposure to moderate cold 

 causes no metabolic increase when shivering is prevented by 

 a strong effort of the will (Loewy). Nevertheless, the ex- 

 planation is inadequate in the case of small animals, such as 

 guinea-pigs, rabbits, and cats ; for very great changes in the 

 metabolism may be brought about by external cold without 

 any outward token of increased muscular activity. Lefevre 

 found that in man also a marked increase in the heat-loss, 

 such as is caused by immersion for a considerable time (one 

 to three hours) in cold water (at a temperature of 7 to 

 I 5 C.), wa s accompanied by a great increase in the produc- 

 tion of heat, so that the axillary temperature fell compara- 

 tively little (e.g., only i C. during a stay of three hours in a 

 bath at 15 C.). With short periods of immersion, a charac- 

 teristic reaction occurs after the person comes out of the 

 bath. The rectal temperature falls to a minimum, which is 

 reached in 20 to 30 minutes after exit from the bath, and then 

 gradually returns to normal. This fall of internal tempera- 

 ture is due to the heating of the superficial portions of the 

 body at the expense of the central portions. By training, 

 the fall of temperature is greatly lessened, the heat-regulating 

 mechanism acquiring, so to speak, with practice, greater 

 promptitude and precision of adjustment. 



It must be admitted, then, that especially in the smaller 

 homoiothermal animals the metabolic changes normally 

 going on in the resting muscles may be reflexly increased 

 without the usual accompaniment of mechanical contrac- 

 tion, and that such an increase of ' chemical tone ' is an 

 important means by which the temperature is regulated. 

 It is possible that other organs besides the muscles may be 

 concerned, though not to a sufficient extent to secure the 

 due regulation of temperature during curara paralysis. It is 

 obvious that in man, whose environment is so much under 

 his own control, a mere automatic regulation is less required 

 than in the inferior animals, and that a regulative power, if 

 present in rudiment, would tend to ' atrophy ' by disuse, or, 

 at all events, become less sensitive to slight changes of tem- 

 perature. In the larger animals, again, mere bulk is an 

 important safeguard against any sudden change of internal 



