as if it were new, and as if the facts hitherto analysed did not already prejudge the solution. Let us begin by giving a definition of sensation from the point of view of experimental psychology.
Sensation, then, is the phenomenon which is produced and which one experiences when an excitant has just acted on one of our organs of sense. This phenomenon is therefore composed of two parts: an action exercised from outside by some body or other on our nervous substance; and, then, the fact of feeling this action.
This fact of feeling, this state of consciousness, is necessary to constitute sensation; when it does not exist, it is preferable to give the phenomenon another name, otherwise the fault is committed of mixing up separate facts. Physiologists have, on this point, some faults of terminology with which to reproach themselves; for they have employed the word sensibility with too little of the critical spirit. Sensibility, being capacity for sensation, presupposes, like sensation itself, consciousness. It has, therefore, been wrong, in physiology, to speak of the sensibility of the tissues and organs, which, like the vegetable tissues or the animal organs of vegetative life, properly speaking, feel nothing, but react by rapid or slow movements to the excitements they are made to receive. Reaction, by a movement or any kind of modification, to an excitement, does not consti-
