INFLUENCE OF THE NEEVOUS SYSTEM. 187 



ed with blushes. Moreover, as experiments have proved, on cutting a 

 nerve the temperature of the parts it supplies declines ; on injuring the 

 great nerve centres the temperature of the whole system lowers, even 

 though artificial respiration may "be kept up. In cases of paralysis, the 

 temperature of the disabled part may be very much lower than that of 

 the sound. A paralyzed arm has shown a surface heat of 70 only, 

 while the sound one has been at 92. It is also said of decapitated ani- 

 mals that they cool quicker when artificial respiration is kept up than 

 when they are let alone. 



All this may be very true, yet it is very far from proving that the 

 nerves are the generators of animal heat. The engineer of a locomotive 

 can regulate the speed of his train and control the production of steam by 

 throwing more or less fuel on the fire, or by supplying it with more or less 

 air ; but does any one impute the production of the heat to him ? If 

 an accident should throw him off, thereby establishing a sort of analogy 

 between his machine and the decapitated animals we have referred to, the 

 stoppage that would soon ensue, and the dying out of the fire, would by 

 no means prove that he made the heat ! 



And so with the nervous system, its function is not a generative, but 

 a controlling one. It determines in what way the combustive or oxidiz- 

 ing actions shall go on, but that is a totally different affair from forming 

 the heat. 



Before specifying more particularly the views I entertain on this sub- 

 ject, I will remark, that the most superficial consideration satisfies us 

 that oxidation in the system goes on in a regulated way. There is not 

 an indiscriminate attack made by the arterial blood on whatever is next 

 before it, but those particles only are removed which the needs of the 

 system require. This therefore implies some overriding or superintend- 

 ing agency, which can save one atom from destruction and surrender an- 

 other. The portion assaulted may, to all appearances, be identical in 

 physical aspect and chemical constitution to an adjacent one that is pass- 

 ed by. There seems to be an arrest or suspension of affinity in one case, 

 and its ready satisfaction in the other. 



There are some well-known facts in natural philosophy which throw 

 a flood of light on this obscurity. If a piece of pure zinc physical anal- 

 be placed in a glass of acidulated water beside a piece of s ies to this 



, 111 ^ i control of the 



copper, so long as the metals are kept apart no action what- nervous sys- 

 ever ensues ; but if a conducting thread is laid from one to tem * 

 the other, the zinc instantly begins to oxidize, clouds of hydrogen gas 

 bubbles rise from the copper, and the thread becomes at once red-hot and 

 magnetic. On lifting the communicating thread all these actions cease ; 

 on restoring it they instantly recur. We think we explain them by say- 

 ing that they are all due to the decomposition of water by the zinc. But 



