It is the same with auditory impressions. The audi tory nerves preserve for a long time the trace of im pressions which have set them vibrating. After a rail way journey, we hear, for several hours after arrival, the noise of the rattling of the carriage. A musical air, and certain favourite refrains, involuntarily resound in one's ears, and that often in a most disagreeable manner.
After long musical seances, says Dr. Moos (of Heidel berg), the sounds persisted for fifteen days in one patient, and in another, a professor of music, for several hours after each lesson.* The gustatory plexuses also seem capable of thus preserving the trace of agreeable or disagreeable im pressions which have affected them, and the intensity of the impression is sometimes lively enough to pro duce, retrospectively, either a secretion of saliva when the mouth waters at the thought of something nice, or, in other circumstances, a sensation of nausea when the substance has produced an unpleasant sensation.
The impressions of general sensibility, olfactory sen sibility, etc., appear to present analogous phenomena.
This species of histological catalepsy, which to some extent polarises the nerve-cells in the situations in which they have been immediately placed at the time of their first impression, is not merely a unique phenomenon, which is met with in the peripheral regions of the nervous system ; it is also met with still more fully developed in the central regions of the system, where it appears with such pronounced and fixed characters that we might say that it governs the manifestations of automatic life in the spinal cord, and directs those of psycho-intellectual activity in the brain.
In the different segments of the spinal cord the per sistence of impressions reveals itself very evidently in the accomplishment of all those co-ordinated move ments which, not being a part of the hereditary patri mony of the motor apparatuses of the organism, are therefore acquired by habit, being the direct product of education.
We know that the greater number of the rhythmic movements we execute in most bodily exercises— dancing, fencing,• playing on musical instruments—are methodical movements which we never accomplish (except the first time) by the intervention of the will ; that they are the effect of long apprenticeship ; that they are only acquired by exercise, the force of habit, and the imitative tendency we have, to reproduce patterns presented to us. Now, our muscles can move
in such marvellous union according to given indications —our movements can be harmoniously combined in accordance with the operations to be accomplished, only by virtue of the latent aptitude of the excito motor cells of the spinal cord for preserving records of the impressions that have first thrown them into agita tion—for remaining for a longer or shorter time in the primordial condition first imposed upon them.
It is, then, our first impressions that vibrate in us like distant echoes of the past, and serve as a stimulus to the excitations of automatic life. It is they that, always alive, always faithful to themselves, are incessantly dis engaged in the form of unconscious reminiscences, regu larly rhythmic motor manifestations, which faithfully reproduce the impression of the primordial excitation.
It is the same persistent excitations, condensed in the sphere of automatic activity, that in certain morbid cases, when the regions of the sensorium and conscious perception are temporarily closed to impressions from without, excite those very curious harmonic movements accomplished by certain somnambulists, which take place 'Will PrOP740, by the simple calling into activity of the automatic regions which act of themselves, and exhibit externally a series of 11.71C011SCiOZIS reminiscences. In connection with this subject, Mesnet has lately re ported a most interesting case—that of a soldier, who, having received a shot in the head, afterwards suffered from very strange symptoms. • This man was subject to a species of somnambulistic crises, in consequence of which his sensorium was to a great extent cut off from all external impressions. He ceased, more or less suddenly, to enter into contact with the surrounding medium, and then, while in this condition, would walk about, go and come, and if any one endeavoured to direct his movements in any definite manner, the impulse was inevitably developed in the direction of former excitations preserved in the state of unconscious reminiscences in the plexuses of his automatic activity.