324 HANDBOOK OF PHYSIOLOGY. 



temperature, and warm-blooded animals then react to variations of the 

 external temperature just in the same way as cold-blooded. These ex- 

 periments seem to suggest that there is a centre, to which, under nor- 

 mal circumstances, the impression of cold is conveyed, and from which 

 by efferent nerves impulses pass to the muscles, whereby an increased 

 metabolism is induced, and so an increased amount of heat is generated. 

 The centre is probably situated above the medulla. Thus in urarized 

 animals, as the nerves to the muscles, the metabolism of which is so im- 

 portant in the production of heat, are paralyzed, efferent impulses from 

 the centre cannot induce the necessary metabolism for the production 

 of heat, even though afferent impulses from the skin, stimulated by the 

 alteration of temperature, have conveyed to it the necessity of altering 

 the amount of heat to be produced. The same effect is produced when 

 the medulla is cut. 



Influence of Extreme Heat and Cold. In connection with the 

 regulation of animal temperature, and its maintenance in health at the 

 normal height, may be noted the result of circumstances too powerful, 

 either in raising or lowering the heat of the body, to be controlled by the 

 proper regulating apparatus. Walther found that rabbits and dogs kept 

 exposed to a hot sun, reached a temperature of 114. 8 F., and then died. 

 Cases of sunstroke furnish us with several examples in the case of man; 

 for it would seem that here death ensues chiefly or solely from elevation 

 of the temperature. In many febrile diseases the immediate cause of 

 death appears to be the elevation of the temperature to a point incon- 

 sistent with the continuance of life. 



The effect of mere loss of bodily temperature in man is less well 

 known than the effect of heat. From experiments by Walther, it ap- 

 pears that rabbits can be cooled down to 48 F. (8.9 C.), before they 

 die, if artificial respiration be kept up. Cooled down to 64 F. (17.8 

 C.), they cannot recover unless external warmth be applied together 

 with the employment of artificial respiration. Eabbits not cooled below 

 77 F. (25 C.) recover by external warmth alone. 



