Changes in the Nervous System.

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frequently opened his eyes, and the breathing became so regular, that many addressed him, but he made no sign of understanding. Nevertheless, by the assistance of a medical student, he took a few steps on the floor, and seated himself in an arm-chair. He seemed like a man intoxicated, and overcome with the exertion he had made. Every effort was put in practice to equalise the circulation; but congestion of the brain eventually came on, and terminated his existence. A man named Clydesdale, who was executed for murder at Glasgow, was also made the subject of a similar experiment.-Harrison on the Medical Aspects of Death.

CHANGES IN THE NERVOUS SYSTEM.

Sir Benjamin Brodie considers it (1) very probable that the Nervous Force is some modification of the force which produces the phenomena of electricity and magnetism; and he compares the generation of it by the oxygenated blood on the grey substance of the brain and spinal chord, to the production of the electric force by the action of the acid solution on the metallic plates in the cells of a voltaic battery.

2. We know that the solid parts of the body are in a state of perpetual change. There is a constant influx of new materials supplied by the digestive organs, and in other ways; and a corresponding efflux of the old materials by means of the various excretions, especially by that of the kidneys. The brain itself forms no exception to the general rule. We cannot otherwise account for its growth in the early part of life, nor for the alterations in its structure which arise as the consequence of disease, nor for those other changes which occur in extreme old age. The mind preserves its identity, but there is no corresponding identity of the corporeal organ with which it is associated; and we may even venture to assert that the brain of to-day is not precisely and in all respects the same with the brain of yesterday, and that it will not be the brain of to-morrow.

3. We cannot suppose that such deposition of new materials and abstraction of old ones can be effected by mere mechanical means, as you would take one brick from a building and substitute another in its place. The elements of which the nervous system is composed exist in the blood, but they must undergo a new chemical combination before they can be incorporated with it; and in like manner they must undergo a chemical change of an opposite kind before they can re-enter the current of the circulation. The precise character of these chemical changes we have no means of ascertaining; but whatever it may, there is reason to believe that it must be in proportion as the nervous system is more or less exercised.,

The nervous substance is distinguished from all the other tissues

(with the exception of the bones) by the very large proportion of phosphorus which enters into its composition, amounting to 1.5 parts in 100, and to as much as one-thirteenth of the solid matter which remains after the evaporation of the water; and that one result of over exercise of the nervous system is the elimination of an unusual quantity of salts containing phosphorus, by means of the secretions of the kidneys. This fact was first observed by Dr. Prout, who has given it as his opinion "that the phosphorus in organized beings is in some measure connected with the nervous tissues and nervous action."

Lastly, Sir Benjamin Brodie considers that even if we had more perfect organs of sense, or more perfect microscopes, we could trace exactly the changes which took place in the brain, we should be just as far from identifying physical and mental phenomena with each other as we are at present. The link between them would still be wanting, and it would be as idle to speculate on the nature of the relation between mind and matter, as on the proximate cause of gravitation, or of magnetic attraction and repulsion.-Selected and Abridged from Psychological Inquiries.

Dr. Forbes Winslow has thus sketched what may be termed the ubiquitous existences of the Nervous System:

From the maggot that leaps from a nut as we crack it in our plate after dinner, and the caterpillar that eats up the leaves of our favourite convolvulus in the garden-from the fish that cleaves the green, translucent wave, and the bird that wings the breeze of incense-breathing morn-from the lion that roams the desert wild, and the horse that tramps the battle field, or prances before the lady's equipage-up to Man, the master of them all, there is one all-pervading Nervous System, progressively diminishing in a downward scale of analytic exhaustion, till it ends in a mere microscopic globule of a brain, by which they all communicate and hold their relative and inter-dependent existences, according to their various forms and needs, and types of organization, function, growth, location, and pursuits.

WORKING OF THE BRAIN.

From several causes within medical experience, it would seem that Motion of the Brain is, at least, coincident with every mental operation. Thus, "in a case reported by Dr. Pierquin, observed by him in one of the hospitals of Montpellier in 1821, he saw, in a female patient, part of whose skull had been removed, the brain motionless, and lying within the cranium, when she was in a dreamless sleep; in motion, and protruding without the skull, when she was agitated by dreams; more protruded in dreams reported by herself to be vivid; and still more so, when perfectly

awake, and especially if engaged in active thought or sprightly conversation."-Combe's Constitution of Man.

A British captain, whilst giving orders on the quarter-deck of his ship at the Battle of the Nile, was struck on the head by a shot, and immediately became senseless. He was taken home, and removed to Greenwich Hospital, where for fifteen months he evinced no sign of intelligence. He was then trephined, and immediately upon the operation being performed, consciousness returned, and he immediately began busying himself to see the orders carried out that he had given during the battle fifteen months previously. The clockwork of the brain, unaware that it had stopped, upon being set going again, pointed to the exact minute at which it had left off. These sudden revivals of a lost intelligence almost rival in their dramatic effect the effect of the Prince's advent in the palace of the Sleeping Beauty, where at the magic of a kiss, the inmates of the royal household, who had gone to sleep for a hundred years transfixed in their old attitudes, leapt suddenly into life and motion, as though they had only for a moment slept.-Once a Week.

WHAT IS MEMORY?

The eye, the ear, and the other organs of sense, are physical instruments by means of which impressions are communicated through the nerves to the brain. It does not, however, follow that the brain itself feels, or that it performs any other than a subordinate office, conveying the impressions received from the organs of sense to a superior principle in connexion with it. Memory is a recurrence of sensations, which existed formerly, produced by the operation of some internal changes, after the causes, by which the first sensations were excited, have ceased to exist. When renewed, sensations are (with some rare exceptions,) fainter and less distinct than those in which they originated. There is also this difference between them, that the renewed sensations are subject to the influence of volition, vanishing at once on the slightest effort being made to direct the attention to anything else; whereas, we have no such power over the impressions which are made on our senses by the immediate presence of external objects.

Notwithstanding these points of difference, it is plain that memory is closely allied to sensation, and the resemblance between the two orders of phenomena is so great as to justify the suspicion that the nervous system is instrumental in producing the one as well as the other; while a multitude of facts show that the suspicion is well founded. A blow on the head may destroy the memory altogether, or (which is more usual), it may destroy it partially, or it may interrupt its exercise for a

certain time, after which it may be gradually, or even suddenly restored. After fever, also, and some other bodily ailments, the memory is not unfrequently impaired or lost. A blow on the head which causes insensibility, generally affects the memory so far that when the patient has recovered from the state of insensibility, he has no knowledge of the accident. (See page 69.) But in some instances, the effect of a blow on the head is merely to disturb the memory, the other functions being unimpaired.

It seems to be a legitimate conclusion, that impressions made on the organs of sense, and transmitted to the brain, produce some actual change in the minute organization of the latter; and that this is subservient, and in our present state of existence, essential to, the memory.

What the actual changes in the condition of the brain may be, it is impossible for us to comprehend.

It is clearly not sufficient that an impression should be transmitted to the brain to be remembered. An act of the mind itself is necessary for that purpose; and that, as Dr. Hooke has observed, is attention. It is only a small proportion of what we see, or hear, or feel, or imagine, that is not immediately forgotten, simply because there are very few of these things to which we pay more than a momentary attention, while to many of them we pay no attention at all. Now, attention implies volition; that is, it is that effort of volition by which an object, which would otherwise have immediately passed away, is kept present to the mind during a certain period of time. Sensation and volition are the two functions by means of which the mental principle is enabled to maintain its communication with the external world. It is under the influence of volition that the contraction of muscles takes place for locomotion, speech, the procuring of food, and other purposes, and that the torpedo discharges his electric battery. Here there is an impulse communicated from the mind to the brain, and from hence to the nerves, and from these to other organs, and producing a marked change in the condition of the latter; and à priori, there is no reason to doubt that the operation of a similar cause may produce an equal change, though of another kind, and more prominent in the minute structure of the brain itself.

It appears probable that there is a special organ in the brain for the purpose of memory, as well as for locomotion and speech. But there our knowledge ends. At present, we must be content to acknowledge that we know nothing as to the locality of the function, nor of the minute changes of organization which are connected with it.-From Sir B. Brodie's Psychological Inquiries.

Persistence of Impressions.

HOW THE FUNCTION OF MEMORY TAKES PLACE.

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Berzelius asks-Where, in the narrow emulsive mass of the Brain lie those registers of the objects and occurrences of a man's life; those tablets which are the result of recitals or reading; the numberless words of many languages understood by the same individual; and the systems of facts belonging to the many sciences which he understands, Where is all this knowledge stored away ready for use? What part has the matter (the water, the albumen, and the cerebral fat) in that sublime activity, which, nevertheless, does not exist without it, and which, through its least derangement, is altered, or entirely lost?

The method of transforming the valuation of time into space by the rapid rotation of a cylinder rotating 1000 times in a second, proposed by M. Fizeau, has been applied by M. Helmholtz to the measurement of the rapidity of nervous impulse. In this way it has been found by experiments made with the utmost care,1. That sensations are transmitted to the brain with a rapidity of about 180 feet per second, or at one-fifth the rate of sound; and this is nearly the same in all individuals. 2. The brain requires one-tenth of a second to transmit its orders to the nerves which preside over voluntary motion; but this amount varies much in different individuals, and in the same individual at different times, according to the disposition or the condition at the time, and is more regular the more sustained the attention. 3. The time required to transmit an order to the muscles by the motor nerves is nearly the same as that required by the nerves of sensation to pass a sensation; moreover, it passes nearly one-hundredth of a second before the muscles are put in motion. 4. The whole operation requires one and a quarter to two-tenths of a second. Consequently, when we speak of an active, ardent mind, or of one that is slow, cold, or apathetic, it is not a mere figure of rhetoric. --M. Ule, Revue Suisse.

PERSISTENCE OF IMPRESSIONS.

There is reason to believe that no idea which ever existed in the mind can be lost. It may seem to ourselves to be gone, since we have no power to recal it; as is the case with the vast majority of our thoughts. But numerous facts show that it needs only some change in our physical or intellectual condition to restore the longlost impression. A woman-servant, for instance, twenty-four years old, who could neither read nor write, in the paroxysm of a fever, commenced repeating, fluently and pompously, passages of Latin, Greek, and Hebrew; and it afterwards appeared that, in her early days a learned clergyman with whom she lived, had been in the daily habit of walking through a portion of his house, that