From the other, the spiritualistic, side of the argument, it has been sought to meet the above considerations by an interesting analogy. Matter (the brain in this case) may, it is urged, be regarded as the instrument by which, under present conditions, Thought manifests itself and acts. You can take a piano and put it out of tune or otherwise damage it, so as to render it incapable of conveying the real mind of the performer, who, nevertheless, remains quite unaffected. The soul is the invisible performer. You can damage the brain so that the soul _can no longer express itself_ under the conditions of our present existence, but it is an entirely unwarrantable inference to say that you have thereby damaged or destroyed the soul itself. The analogy of physical energy will make this clear. You can make an engine work by the oxidization of coal, but this process can only loosely be described as the source of the energy which is manifested by the engine. All that one does by burning the coal is to turn potential energy into active or kinetic energy. When the engine goes to pieces, or the coal burns out, not a particle of energy is lost; it merely goes back into the shape of potential energy again. I think this reply is substantially a sound and effective one. At the same time it must be allowed that the physiological argument is more subtle than is usually recognized by those who try to meet it as above. You may so damage a piano as to render it incapable of being properly played on—you may get from it the incoherent janglings of insanity, without affecting our belief in the existence of a real musician behind these unintelligible manifestations. But how if it can be shown that certain mechanical alterations will result, not in nonsense but, let us say, in bringing out mere Offenbach when the performer has always hitherto been wont to play Beethoven? A simple injury to the instrument, it may justly be argued, has no such vital significance as this change in the nature of the thing expressed. Shall we not have to conclude that the man really _is_ the instrument, that the mind is a phenomenon accompanying the temporary combination of certain material constituents, lasting only as long as that combination shall endure and varying _pro tanto_ with everything that causes it to vary?