excitations which have in the first place set them in action, thus storing up within themselves phosphorescent traces, which are records of the received impressions.

3. Automatism, which expresses the spontaneous reactions of the living cell, which sets itself in motion of its own accord (motu proprio), and in an unconscious and automatic manner expresses the different states of its sensibility thrown into agitation.

It is the history of these various general properties of the nervous elements that we are now about to study in due course, in the physiological part of this work. These properties once defined and known, we shall attack the study of the different combinations to which they adapt themselves by combining one with another; and thus, proceeding from the known to the unknown, from the simple to the composite, we shall advance with better ascertained points of support into that domain, so complex, and at the same time so rich in interesting prospects that of cerebral activity proper.

BOOK I.

SENSIBILITY OF THE NERVOUS ELEMENTS.

CHAPTER I.

GRADUATION AND GENEALOGY OF THE PHENOMENA

OF SENSIBILITY.

SENSIBILITY 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 motu proprio, 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 repulsion 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 molecules 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 substance 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 nervecells being as yet extant.*

Little by little, as the living cells group together and form more dense agglomerations, the phenomena of sensibility 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

* Naturalists have made known to us beings of an organization so simple that their entire body is formed of but one cell. Their whole development, their whole existence, is shut up within limits thus strict. We may mention the gregarines in particular. (Frey, "Histologie et Histochemie," p. 74.)

ties and avoid such as are inimical to them. It regulates 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 impressions 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 phenomena 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,

* The gregarines, which are met with in troops as living parasites in the alimentary canal of insects and other animals, are not only destitute of a mouth, but even of vibratile cilia. They are simple cells with apparent nuclei. (Hartmann, "Conscience des plantes." Revue Scientifique," July 1873, p. 623.)

Plants which catch insects are sensitive to the touch; climbing plants discern points of support. The leaf of the vine feels the light, towards which it strives to turn the right side, and every flower feels it, and strives to bend its head towards it. The mimosa feels and reacts. every motion that it shall be preceded by sensibility. p. 625.)

It is the essence of (Hartmann, loc. cit.,

under the excitement of a light touch apply themselves to the pistil; the flowers of the water-lily hide themselves at the bottom of the water while they wait for the day. It is even more astonishing to see what happens 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.*

Like an animal, it feels and reacts on the contact of the lightest touch; feels inequalities of temperature;+ is influenced and struck with anæsthesia by the inhalation of chloroform; like an animal, moreover, its sensitive unity forms a complete whole; its leaflets and 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.

* Marked movements are performed every evening by vegetables with composite leaves, like the cytisus or robinia pseud-acacia. We see these plants make their preparations for night every evening-some simply fold their leaves, others, with more foresight, prudently enclose their flowers. The great lotuses of the Nile, and the water-lilies of our own lakes, draw down their carefully closed corollas to the bottom of their waters; and the sun must have come next day to illumine the earth before the chilly and sleeping plant consents to open its petals.

The sleep of plants is related to the greater or lesser intensity of the light with which they are surrounded; and, what is more conclusive, plants which have been strongly illuminated at night, while they are in obscurity during the day, have changed their habits so as to sleep in the day and wake at night. (Edmond Grimard, "De la sensibilité végétale." "Revue des Deux Mondes," 1868, p. 379.)

† Grimard, loc. cit., p. 385.