ITS SCOPE AND METHOD 77 



to nervous action may mean that the nervous activity 

 is not immediately based on purely chemical change. 

 In the concentration cell we have an instance of electrical 

 energy which, though arising from chemical solutions, 

 arises from them not from chemical reaction but in virtue 

 of changes comparable with the simple expansion of a gas. 

 If electrical disturbance is the cardinal function of nerve, 

 we are not so little advanced in essential knowledge of 

 the activity of the nervous system as would otherwise 

 appear. 



And the factor of nerves in the mechanism of our 

 temperature regulation brings naturally the question ; 

 Are our sensations of temperature part of this mechanism ? 



Now since the temperature of all but the very surface 

 of the body does not change whether we are exposed to 

 heat or cold, it is obvious that when we feel hot or cold 

 the sensation arises not from the depth but from the 

 surface layer of the body. Again, though a man's in- 

 ternal temperature may not be affected one degree in 

 travelling from the arctic region to the equator, yet it 

 will alter much even while he sits at home if he ' catch 

 cold' he then becomes 'feverish'. At the outset of 

 fever he feels ' chilly ', although his internal temperature 

 is higher than usual. A spasm of the blood-vessels of 

 the skin makes the skin cold as it would be in a cold 

 draught. It seems clear that our sensations of cold and 

 warmth arise from nerves distributed to the skin and 

 not to the deep organs. 



But it would be wrong to suppose that it is these 

 sensations which regulate the temperature of the body. 

 That regulation, accurate and smoothly-working as it is, 

 is not a volitional regulation. It is automatic. We can 

 assist it, but we cannot govern it further. True, we are 

 disinclined to take active exercise in extreme heat ; and, 



