At the moment, indeed, when the external impres sion sets the peripheral sensorial cells vibrating, these are affected, according to the different modes of their natural sensibility. They are sensitized in a different manner, according as the excitation is agreeable or disagreeable to them. In the first case a sensation of pleasure accompanies the external impressions, in the second case a sensation of discomfort ; so that the nervous element coming into play with its latent activity, transports to the sensoriunz, not only the an nouncement of the arrival of the external excitation, but at the same time the special notion of pleasure or pain related to each excitation.
Every former impression, every reminiscence that slumbers within us, remains there from the moment it has been perceived, stored up with a specific coefficient which recalls to us the joy, the pain—or even the indif ference of these same peripheral plexuses at the moment when it was incorporated with them and when it began to live in their own life.
We all know that the reminiscence of physical pain, and corporeal chastisement, so lively in animals that are in training, is for man one of the surest guides of his conduct, and a most faithful warning to avoid faults which will inevitably provoke their recur rence.
We know, conversely, that reminiscences of agreeable impressions, and those which have given us most joy, are also those which have the deepest roots in us, and that in fact different states of emotivity, associated with the arrival in the sensorium of such and such a group of external impressions, are what perpetuate themselves with the greatest tenacity. They thus become, as regards the desires they excite or the aversions they beget, the natural pivots around which all human activities gravitate.
2. We have just seen the mode of genesis and trans mission of persistent sensorial impressions, at the mo ment when they are begotten in the peripheral regions of the system—let us now see how they are received in the plexuses of the sensorium, and what reactions they provoke as their consequences.
The connections between the peripheral plexuses and those of the sensorium are so intimate that, so soon as an impression has been produced in the former, their partner central regions immediately enter into unison with them. There is a nervous condition of similar
pitch which harmonizes one part with another, and whenever the primordial impression has been sufficiently intense, and sufficiently prolonged, whenever there has been an effective participation of the nervous plexuses laid under contribution, the partner plexuses of the sensorium sympathetically associate in their excitations and enter upon a concordant period of erethism. The incident excitation arrives then in the plexuses of the cortical substance, purified and animalized by the peculiar metabolic action of the nervous plexuses in the womb of which it is incarnated, and then, transforming itself into psychic excitation, it develops the latent energies proper to the cerebral cells, imprints itself upon them, and perpetuates itself in them in the form of per sistent vibrations, like a phosphoric gleam of the ex ternal world.
Thus. it is, that this mysterious property which the nervous elements possess—that of persisting in the vibratory condition in which they have been placed— is here again found consistent with itself throughout the different stages traversed by the sensorial excitations ; from the peripheral regions where it reveals itself in so indubitable a manner (as in the persistence of impres sions on the retina), to the central regions, where it acquires characters entirely dependent upon the multi tude of elements which serve to maintain it.
Thus it is then, that external impressions of all kinds, the diverse emotions we have felt, become finally attenu ated in the plexuses of the sensorium, and in the form of persistent vibratory thrills become the posthumous expressions of impressions and past emotions which remain alive in is when the primordial excitations have long ago disappeared.
Sensorial excitations, when they are diffused in the plexuses of the sensorium and fix themselves there in a persistent manner, do not usually remain there in the state of vague, uncertain impressions. They go further, penetrate more deeply into the recesses of cerebral life, and when they are sufficiently lively and often enough repeated, they penetrate even into those inmost regions where the notion of conscious personality is elaborated,' and thus become conscious reminiscences of ancient emotions that have thrilled us.