ELEMENTS.
automatic activity of the nervous elements, like their histological sensibility, is merely one of the special forms of their peculiar vitality.
Diffused, in a similar manner, in its most simple forms, through the most elementary organisms, this automatic activity is perfected, and amplified, in proportion as it is distributed through more abundant and more dense agglomerations of cells, which are at the same time endowed with a more intense vital energy.
It reveals itself in its most simple forms, as a histologic property of the free cells, the white corpuscles of the blood ; of that series of cells with 'mobile pro longations (vibratile cilia, spermatozoids), whose auto matic energy is manifested in such characteristic amoeboid movements ; and finally of isolated masses of protoplasm.
As we ascend in the zoological series, we perceive that the manifestations of automatic life consist not merely in purely local phenomena, in which the histologic ele nients accomplish the natural phases of their evolution motu proprio, but in the exhibition of new dynamic properties. The histological elements, then, secrete, as it were, at the expense of their substance, peculiar autogenic excitations, and project them to a distance in the form of a continuous or interrupted current, thus acquiring a species of power of radiating to a distance the vital forces they have locally evolved.
Thus we see electric fishes accumulate, in special tissues of their organism, the electric force which they emit, for the purpose of defence, in the form of dis charges regulated by a voluntary excitement.* Thus also we see the superior animals condense in the nervous plexuses of their organism stores of motor influence, to be distributed through the peripheral regions in the form of complex manifestations of voluntary motor-power, or of the motor-power of vegetative life.
The operations of automatic activity are, then. generally characterized by a series of processes inverse to those of sensibility. In fact while the phenomena of sensibility are usually characterized by centripetal currents which pass from the peripheral regions where they are conceived towards the nervous centres, the phenomena of automatic activity, on the contrary, are marked by currents with a centrifugal direction. With the former they complete the cycle, and reflect outwards the excitations which arrive from the external world through the sensitive regions.
Now if we consider the phenomena of automatic activity, from the point of view of their relations, and their connections with the nervous system, we see that for them also, for the organic force which excites them, the nervous system similarly plays a perfecting part, that it amplifies them, gives them its own energy, places at their disposal its conducting filaments, and thus enables them to reach their highest point of perfec tion.
They follow indeed, step by step, the progressive stages of development of the nervous apparatuses with which they are connected. Thus, in the peripheral
regions of the system, where the phenomena of vege tative life take place by means of automatic forces alone, the nervous elements—represented by the unicel lular sympathetic ganglions, which are like so many little outposts in the web of the tissues—interfere only occasionally to regulate the different rhythms of the local circulations.
In these distant regions the automatic life of the individual elements reigns without contest. It is local activity that rules here ; and a sort of complete decen tralization characterizes the life of these regions.* Little by little as we approach the centres a progress towards complete subordination takes place in the distribution of the living forces of nervous activity. Thus, if we pass from the ganglions to the medulla, we observe that sensitive phenomena are distributed in certain regions, and motor phenomena in others. Sensibility and automatic activity, which were vaguely fused together in the peripheral ganglionic masses, are here distinctly separated, and exercise their functions regularly by means of nervous cell-territories specially adapted for a determined end. This is still not all ; in the brain this principle of the progressive perfection ment of physiological work by the complexity of the apparatuses by which it is accomplished, becomes more and more evident ; so that automatic activity is re vealed not only in the phenomena of motor-power, but also in the manifestations of psycho-intellectual activity.
Wherever, in fact, the phenomena of nervous life are developed, they appear not only with those general characters of individual sensibility and organic phospho rescence which we have hitherto recognized as being the essential attributes of every living nerve-cell, but with a new co-efficient in addition—that property, so charac teristic of automatic activity, the capacity for spon taneous vibration, if their natural sensibility, previously aroused, be thrown into agitation, and for radiating and projecting to a distance the expression of that histologic sensibility thrown into agitation—at first in the form of an automatic reaction completely independent of the existence of the nervous system, and subsequently in the form of nervous discharges.
The automatic activity of every living cell is, then, nothing but the spontaneous reaction of its individual histological sensibility, evoked in some manner or another.
This special form of the vitality of the nervous elements we are now about to consider. We shall thus see that these automatic activities, together with sensibility and organic phosphorescence, become the fundamental elements of cerebral activity ; that they associate one with another in a thousand ways, and combine to pro duce the most complex operations of cerebral dynamics; and that they always underlie most of the operations of cerebral life.