is that fundamental property which characterizes the life of cells. It is by means of it that the living cells come into contact with the medium that surrounds them, and that they react vzotztproprio, by virtue of their natural affinities which are thrown into agitation, and exhibit a desire for the excitations which gratify them, and a repulsion for those that are unpleasant to them. Attraction for agreeable and re pulsion for disagreeable things are the indispensable corollaries of every organism fitted for life, and appa rently the elementary manifestation of all sensibility.
Sensibility, which is, perhaps, itself, in the organic world, only the transformation of those blind forces, which attract among themselves the crystalline mole cules of the inorganic world, and group them according to their proper affinities ; this phenomenon, sensibility, begins to appear, in its most simple forms, with the first rudiments of life.
It is in the unicellular organisms of the vegetable kingdom that it first embodies itself and reveals itself in its own shape ; and here it shows itself as a property of tissue, very distinctly connected with the very sub stance of the amorphous protoplasm of which it is the endowment, under the form of vague diffuse contractility, no special element being reserved for it, and no nerve cells being as yet extant.* Little by little, as the living cells group together and form more dense agglomerations, the phenomena of sen sibility become more distinctly evident, and soon we find them provided with special apparatuses designed to serve them as a support, and to condense and perfect their modes of activity ; while in the superior animals they become more and more highly endowed, to arrive at man as the last term of their long evolution, and produce those phenomena so rich, so varied, so delicate, defined in concreto under the name of the moral sense.
In this chapter we shall follow the process of the evolution of sensibility, from the most elementary phases under which it shows itself at its point of origin, to the moment of its most complete expansion in man.
Sensibility, we may say, in its most simple revelations in unicellular organisms, at first appears in a vague and undetermined form. It reveals itself by that essential tendency which these protorganisms have, to seize upon substances which gratify their natural affini ties and avoid such as are inimical to them. It regu
lates and governs the continuity of the purely trophic phenomena of the life of cells.* In vegetables the phenomena of sensibility have already taken more distinctly marked forms. Their cycle is no longer restricted to the local operations of rough and ready assimilation and disassimilation.
Vegetable cells, even when agglomerated in but small groups, have become sensitive and impressionable by external agents. Calorific and luminous impres sions produce a certain effect upon them, and if this effect be grateful to certain natural affinities, we may see them gradually inclining in the direction from whence these excitations come. They turn automatically towards the sun, awake with him when he appears, sleep when he has disappeared, and, in a word, present that series of unconscious and graduated movements by virtue of which they tend towards the realization of their latent satisfactions.t Botanists have already described those curious phe nomena of vegetable sensibility by virtue of which we see the petals of certain flowers fold up at night and unfold in the day time ; the stamens of the barberry, under the excitement of a light touch apply themselves to the pistil ; the flowers of the water-lily hide them selves at the bottom of the water while they wait for the day. It is even more astonishing to see what hap pens with sensitive plants, and to observe how that curious vegetable, mimosa pudica, presents in itself all the most delicate manifestations of the impressionability of living beings.4 Like an animal, it feels and reacts on the contact of the lightest touch ; feels inequalities of temperature ;-f is influenced and struck with by the in halation of chloroform ; like an animal, moreover, its sensitive unity forms a complete whole ; its leaflets *nd rootlets are united in such an intimate consensus that if its rootlets be subjected to the action of any irritant, its leaflets are affected at the same time, and sympathize painfully with their sister cells of the lower regions which have been thrown into agitation ; just as we see that sensibility when developed in any region of an animal whatever, has a generalized reaction all over the organism.