THERMIC NERVES. 457 



case with parts, like the skin, in which the blood is cooled. 

 An organ colder than the blood is of course warmed by 

 an increase in its circulation, as seen in the local rise of tem- 

 perature in the skin of the face in blushing. 



Thermic Nerves. All nerves, such as motor or secre- 

 tory, which can throw working tissues into activity are in 

 a certain sense thermic nerves: since they excite increased 

 oxidation and heat production in the parts under their con- 

 trol. A true, purely thermic nerve would be one which 

 increased the heat production in a tissue without otherwise 

 throwing it into activity; and whether such exist is still 

 undecided. Certain phenomena of disease, however, seem 

 to render their existence probable. If we return for a 

 moment to our former comparison of the working Body to 

 a steam-engine, such nerves might be regarded as agencies 

 increasing its rate of rusting without setting it at work. 

 The oxidation of the iron would develop some heat, but by 

 processes useless to the steam-engine, although such are, 

 in moderation, essential to living cells; the vitality of 

 these, even when they rest, seems to necessitate a constant, 

 if small, breaking down of their substance. In an amoeboid 

 cell no doubfc such processes occur quite independently of 

 the nervous system; but in more differentiated tissues they 

 may be controlled by it. Just as a muscle does not nor- 

 mally contract unless excited through its nerve, although 

 a white blood corpuscle does, so may the natural nutritive 

 processes of the muscle-fibre in its resting condition be de- 

 pendent on the nerves going to it. If these be abnormally 

 excited the muscle vvill break down its protoplasm faster 

 than it constructs it, and consequently waste; at the 

 same time the increased chemical degradation of its sub- 

 stance will elevate its temperature. Febrile conditions, in 

 which many tissues waste, without any unusual manifesta- 

 tion of their normal physiological activity, would thus bo 

 readily accounted for as due to superexcitation of the 

 thermic nerves. Moreover, it is found that lesions or sec- 

 tions of the spinal cord are followed by a rise in the tem- 

 perature of those parts of the Body supplied with nerves 

 arising below the diseased or divided portion. Now 



