198 ANIMAL HEAT. 



The influence of the nervous system in modifying the produc- 

 tion of heat has been already referred to. The experiments 

 and observations which best illustrate it are those showing, 

 first, that when the supply of nervous influence to a part is 

 cut off, the temperature of that part falls below its ordinary 

 degree ; and, secondly, that when death is caused by severe in- 

 jury to, or removal of, the nervous centres, the temperature of 

 the body rapidly falls, even though artificial respiration be 

 performed, the circulation maintained, and to all appearance 

 the ordinary chemical changes of the body be completely ef- 

 fected. It has been repeatedly noticed, that after division of 

 the nerves of a limb, its temperature falls ; and this diminution 

 of heat has been remarked still more plainly in limbs deprived 

 of nervous influence by paralysis. For example, Mr. Earle 

 found the temperature of the hand of a paralyzed arm to be 

 70, while the hand of the sound side had a temperature of 

 92 F. On electrifying the paralyzed limb, the temperature 

 rose to 77. In another case, the temperature of the paralyzed 

 finger was 56 F., while that of the unaffected hand was 62. 



With equal certainty, though less definitely, the influence of 

 the nervous system on the production of heat, is shown in the 

 rapid and momentary increase of temperature, sometimes 

 general, at other times quite local, which is observed in states 

 of nervous excitement ; in the general increase of warmth of 

 the body, sometimes amounting to perspiration, which is ex- 

 cited by passions of the mind ; in the sudden rush of heat to 

 the face, which is not a mere sensation ; and in the equally 

 rapid diminution of temperature in the depressing passions. 

 But none of these instances suffices to prove that heat is gen- 

 erated 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 

 bloodvessels (p. 121), the quantity of blood supplied to apart; 

 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 involv- 

 ing 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 temperature, 

 and its maintenance in health at the normal height, it is in- 

 teresting to note the result of circumstances too powerful, either 

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



