In the adult the elements of cerebral activity in a condition of complete development are endowed with all the energies they are capable of assuming. They do not now behave as they did in the young child during the period of his evolution, as far as regards the preservation and storing up of external excitations.

The period of saturation begins for the cerebral cell. The power of retention of external excitations is already on the brink of decay. New acquisitions of heterogeneous elements which do not form a portion of the circle of youthful knowledge become very difficult, if not impossible. We know how painful the labour of learning a foreign language, so easy for the young child, becomes for the adult; how rebellious the memory is as regards the registering of new words; and with what an expenditure of intellectual force we retain the vocabulary of languages with which we were not familiar in childhood. We also know how blunt, even in the domain of common things, the retentive power of our memory, and consequently our powers of application in general, become, if we have to learn. things that are quite new to us; and how, for instance, we with reason look upon it as impracticable to acquire a special technical education, and commence a new career after forty years of age.

At this period of life first impressions still faithfully persist in the memory, but nevertheless they have a tendency to diminish in intensity, and it is necessary to vivify them by incessant labour, to stimulate them anew by placing the cerebral regions where they are stored up in identical conditions, by similar impressions of equal intensity, so as to prevent their becoming extinct; just

as we keep up a fire by continually supplying it with fresh material.

As the entire human frame begins to suffer from the effects of senescence, which occurs in different individuals at very different periods, the cerebral cells, like the other elements of the organism, suffer a premature decay.

They grow old histologically; they become more of less infiltrated with fatty granular matter; they cease to be transparent, shrivel up, and from a dynamic point of view insensibly lose a portion of their sensibility and their special retentive power; so that, as foci of organic phosphorescence, it may be said that they are extinguished within certain circumscribed localities of the cerebral cortex, and consequently cease to preserve a record of their first impressions. Thus it is that the general phenomena of mental activity undergo a perceptible decay proportional to the sum of the cerebral elements superannuated. In the aged, memories sometimes disappear in an isolated manner; sometimes those which are not maintained by regular exercise become extinct; sometimes the general faculty of memory fails altogether, and in its decay involves the progressive blunting of the most lively sentiments.

A strange phenomenon now occurs we perceive, contrary to what à priori would seem most probable, that in old persons, as in patients with dementia, old memories remain the freshest and most vivid, while recent facts, impressions which occur at the very moment, are unperceived and treated as if they did not exist. It is probable that at this period of life, the cells of the sensorium, altered in their essential constitution, have become lazy, and incapable of erecting themselves

in the presence of recent external impressions; and that this state of torpidity of the elements of the sensorium for new excitations, leaves the field free to the older ones which, not being obscured by more lively impressions, continue to vibrate without opposition, and thus perpetuate the last phosphorescent gleams of a far-off past which is dying.*

* Thus, in some old persons in dementia, from the mere fact of the nonabsorption of recent impressions into the sensorium, the notion of the passage of time is completely annihilated.

From the fact that the daily work of the absorption of new impressions has ceased, the individual remains fixed in one spot, as it were, in a cataleptic state, with the ideas and preoccupations that he had at a given moment of his existence. Thus, we see a great number of patients who, having been some ten or twelve years in an asylum, still keep the ideas they had at the moment of their entrance, without having an idea of the passage of time; and who, if asked how long they have been there, will speak of two or three years.

CHAPTER V.

FUNCTIONAL DISTURBANCES OF THE PHENOMENA

OF MEMORY.

THE manifestations of memory, looked at as we have just done, do not then present themselves merely as a collection of simple phenomena, nor as the direct resultant of the impression made upon the plexuses of the cortical substance by an external excitation. They consist in true physiological processes, which have an origin and a regular evolution throughout the nervous system. They demand the active participation of the cerebral cell; and to be regularly executed they must obey certain organic necessities, and the inevitable conditions of integrity and co-operation of the organs through which they effect their complete development.

When, therefore, any disturbance whatever occurs either in the essential vitality or in the constitution of the organic elements which they lay under contribution, the processes of memory are ipso facto disjointed, and that faculty is thus maimed in one or other of the operations that constitute it.

Thus there are circumstances in which that property which the nervous elements possess, of retaining a record of external excitations which have formerly impressed them, attains a condition of extreme and permanent

exaltation. This vibratory phase of their existence perpetuates itself and becomes a species of unsubduable erethism.

All phyiologists, indeed, have recognized the important part a sudden emotion, such as terror or the sight of an epileptic attack,* plays in the production of convulsive seizures; and I have further pointed out that violent impressions may remain stereotyped in certain individuals attacked with general paralysis, and that the shock caused in the sensorium may be very vivid, since it is capable of manifesting itself for several consecutive months in a species of cataleptic condition, imprinted upon the countenance, and upon the attitudes of the body.t

The symptoms presented by the automaton whose interesting case has been reported by Mesnet, come under this class of facts. There are in such cases persistent impressions, which have been formerly accumulated in the automatic sensorium, which continues to direct the excito-motor processes without participation of the conscious personality.

Van Swieten, who was seized with vomiting on coming upon the dead body of a dog which exhaled an insupportable stench, chanced upon the same spot some years afterwards. The memory of what he had experienced produced the same disgust and the same consequences.

This class of morbid phenomena is always developed by virtue of the same physiological processes as those * See Luys, "Actions réflexes cérébrales," p. 83. Morbid phenomena resulting from a persistent impression. (Paris, 1854.)

+ Luys, loc. cit., pp. 73 and 87.

"Annales Medico-psychol." 1851, p. 242. Fact cited by Parchappe.