ELEMENTS.
phenomena of the life of the nervous centres, spite of their apparent complexity, are nevertheless regulated by laws which are in general simple— common principles, which indisputably give them an air of near relationship. These common principles are, moreover, themselves reducible to elementary vital pro perties, which form the basis of each of them in par ticular, and constitute, in a manner, the simple prim ordial principles which we constantly find underlying every combinaticin of nervous activity, however com plicated it may be. These fundamental properties, which thus serve as elementary materials for every dynamic action of the system, may at the present day be thus epitomized, under three principal heads : I. Sensibility, by which the nerve-cells feel excitation from without, and react in consequence, by virtue of the excitement of their natural affinities.
2. Organic Phosphorescence, by which the nervous elements, like bodies which have received the vibrations of light, preserve for a prolonged period traces of the 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 (mote 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 com plex, and at the same time so rich in interesting pros pects--that of cerebral activity proper.