1 82 NATURE AND MAN. 



of animal heat seem to indicate that nerve-force may directly 

 produce elevation of temperature, and there are forms of animal 

 luminosity which do not appear to depend upon an ordinary 

 combustive process, but which rather resemble electric scintil- 

 lations and seem immediately dependent on an exertion of nerve- 

 force. Further, the pecuhar influence of states of the nervous 

 system upon the composition of various secretions can only be 

 explained by supposing that nerve-force has a direct power of 

 modifying chemical action. So that of this, the highest form of 

 vital force, all the material manifestations are of a kind that bring 

 us back again into the region of physics and chemistry. 



But there is another aspect under which we have to view 

 nerve-force — that of its relation to mental phenomena. That the 

 excitement of this force in a certain part of our nervous apparatus 

 is capable of producing a change in our state of consciousness, is 

 the only explanation that can be offered of our recipience of 

 Sensations from impressions made upon our organs of sense. So, 

 again, that the state of mental activity which we term the Will, 

 can so excite the nerve-force of the central organs as to occasion 

 its transmission to the muscular apparatus, is the only explanation 

 that can be offered of our power of voluntary motion. These two 

 simple facts seem quite adequate to establish a " correlation " 

 between nerve-force and mental agency, which is not less com- 

 plete than that which has been shown to exist between nerve- 

 force and electricity ; and we are led to the same conclusion by a 

 careful appreciation of the fact, which all physiological knowledge 

 of the conditions of mental activity tends to establish, that this 

 activity, like exertion of muscular force, can only be sustained, 

 as man is at present constituted, at the expense of the death and 

 disintegration of the nervous substance. This idea of " correla- 

 tion " once started, is found to give a scientific expression to a 

 vast mass of facts demonstrative of the intimate connection 

 between body and mind, which, though accepted as conformable 

 to the universal experience of mankind, have not yet found their 

 place in systematic treatises ; since they occupy that " debatable 

 "ground" between metaphysics and physiology which the votaries 

 of each of these sciences, far from wishing to claim it for them- 

 selves, are desirous to cede to the dwellers on the other side 



