INFLUENCE OF NERVOUS SYSTEM. 251 



of the paralysed finger was 56 F., while that of the un- 

 affected hand was 62. 



With equal certainty, though less definitely, the in- 

 fluence 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 excited 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 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 influence of the 

 nervous system alters, indirectly, the chemical processes 

 from which the heat is commonly generated. There are 

 ample proofs that the nervous system, especially in the 

 most highly organized animals, does so modify all the 

 functions of organic life ; and it appears more reasonable 

 to suppose that it thus influences the production of heat, 

 than to ascribe to it any more direct agency. 



The temporary increase of heat in a part, as in the 

 instances mentioned above, is no doubt in great measure 

 due to a larger influx of blood to the part, in consequence 

 of temporary relaxation of the walls of the small arteries 

 through nervous agency. M, Bernard, for example, found 

 that when he divided, on one side of the neck, the trunk 

 which unites the sympathetic ganglia, or when he removed 

 the superior cervical ganglion, an increase of temperature 

 at once took place on the corresponding side of the face, 

 and continued for many months. This observation has 

 since been abundantly confirmed. It will be more fully 

 considered when speaking of the physiology of the sympa- 

 thetic nerve. 



In the foregoing pages, the illustrations of the power of 



