In like manner, " nervous energy, or that form of force, which, on the one hand, stimulates a muscle to contract, and on the other, appears in forms called mental," is merely physical. It comes from the food we eat. It moves. The rate of its motion is deter- mined to be ninety-seven feet in a second. Its effects are analogous to those of electricity. It is, therefore, for these and similar rea- sons, infei-red that " nerve-force is a transmuted potential energy." This is no less true of nerve-force when manifested in the form of thought and feeling. Every external manifestation of thought- force, argues Professor Huxley, is a muscular one, and therefore analogous to other forces producing similar effects. Besides, it has been proved that every exercise of thought or feeling is attended by an evolution of heat, which shows that thought is resolved into heat. " Can we longer doubt, then, that the brain, too, is a ma- chine for the conversion of energy ? Can we longer refuse to believe that even thought is, in some mysterious way, correlated to the other natural forces ? and this, even in face of the fact that it has never yet been measured ? " ^
To unscientific men of ordinary intelligence, to men not devoted to the study of the sensuous, it is a matter of astonishment that such arguments should be regarded as valid. Admitting all the above facts, what do they prove ? Admitting that animal heat is the same in soiu'ce and nature with heat outside the body ; admit- ting that muscular power is physical in its nature and mode of production ; admitting that nerve-force is also physical ; what then ? Do these facts give any solution of the mysteries of life, if organization, alimentation, or reproduction ? Do they in any measure account for the formation of the eye or ear ; for the mutual relations and interdependence of the organs of the body ?
1 See Professor Barker's Lecture, above referred to, for a summary of these argnmenta, page 24.