244 ANIMAL HEAT. 



the sudden rush of heat to the face, which is not a mere 

 sensation ; and in the equally rapid diminution of tem- 

 perature in the depressing passions. But none of these 

 instances suffices to prove that heat is generated by mere 

 nervous action, independent of any chemical change ; all 

 are explicable, on the supposition that the nervous system 

 alters, by its power of controlling the calibre of the blood- 

 vessels (p. 141), the quantity of blood supplied to a part; 

 while any influence which the nervous system may have in 

 the production of heat apart from this influence on the 

 blood-vessels, is an indirect one, and is derived from 

 its power of causing nutritive change in the tissues, which 

 may, by involving the necessity of chemical action, involve 

 the production of heat. The existence of nerves, which 

 regulate animal heat otherwise than by their influence 

 in trophic (nutritive) or vaso-motor changes, although by 

 many considered probable, is not yet proven. 



In connection with the regulation of animal tempera- 

 ture, and its maintenance in health at the normal height, 

 it is interesting to note 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 a board 

 and exposed to a hot sun, reached a temperature of 

 1 14-8 F., and then died. Cases of sunstroke furnish us 

 with similar examples in the case of man ; for it would 

 seem that here death ensues chiefly or solely from elevation 

 of the temperature. In a case related by Dr. Gee, the 

 temperature in the axilla was 109-5 F. : and 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. before they die, if artificial 



