by action is exhausted, the energizing will be attended with proportionate pain.
It may be a question whether "nerve-force" is the best term to apply to the condition I have spoken of. It is one which opens up the many controversies which exist, and have existed, as to. the nature of force, the relations of the various physical forces, and of these to the forces which we see at work in living animals. While, on the one hand, some shrink away from the very name of force, and will none of it, as a metaphysical entity to be relegated to the schoolmen along with that other metaphysical entity, the "mind" itself, on the other, it is to be feared that men have imagined that the study of mental phenomena has, at length, attained to the rank of the exact sciences, because they have placed nerve-force in the same category and correlated group as light, heat, gravity, and electricity. "Animal combustion," says Mr. Bain, "maintains nervous power, or a certain flow of the influence circulating through the nerves, which circulation of influence, besides reacting on the other animal processes, muscular, glandular, etc., has, for its distinguishing: concomitant, the mind. The extension of the correlation of force to mind, if at all competent, must be made through the nerve-force, a genuine member of the correlated group." It may be interesting to see in what way another distinguished philosopher connects the forces of purely physical phenomena with those of life and animal movement. In his work on Heat (p. 499), Prof. Tyndall writes: "The grand point, permanent throughout all these considerations, is that nothing is created. We can make no movement which is not accounted for by the contemporaneous extinction of some other movement. And, how complicated soever the motions of animals may be, whatever may be the change which the molecules of our food undergo within our bodies, the whole energy of animal life consists in the falling of the atoms of carbon and hydrogen and nitrogen from the high level which they occupy in the food to the low level which they occupy when they quit the body. But what has enabled the carbon and the hydrogen to fall? What first raised them to the level which rendered the fall possible? We have already learned that it is the sun. It is at his cost that animal heat is produced and animal motion accomplished."
When I speak of there being in each nerve cell or centre a condition, varying within certain limits, according to which it is capable of energizing more or less readily and pleasantly, I am far from intending to convey a not ion of any metaphysical entity, even if I use the term "nerve-force." It is not possible to separate this force in kind from that which is the special property of the cell. Each cell, as it lives its life in our bodily organization, as it grows to maturity, and fades in its decay, separates and selects from the blood, by a molecular metamorphosis, that which it requires for its function as an idea-cell, a hearing, or a sight cell, but it separates it in varying quantity and
