ANIMAL HEAT. 317 



urari, exposure to cold diminishes both the metabolism and the temper- 

 ature, and warm-blooded animals then re-act to variations of the ex-, 

 ternal temperature just in the same way as cold-blooded. These experi- 

 ments seem to suggest that there is a centre, to which, under normal 

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

 efferent nerves impulses pass to the muscles, whereby an increased metab- 

 olism 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 important 

 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, when 

 tied to aboard and 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 inconsistent 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 appears that 

 rabbits can be cooled down to 48 F. (8.9 C.), before they die, if arti- 

 ficial 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. Rabbits not cooled below 77 F. 

 (25 C.) recover by external warmth alone. 



