The Brain and its Functions

J Luys

• Publisher: Routledge
• Year: 2020
• Print ISBN: 9780367259723
• eBook ISBN: 9781000697520
• Edition: 1
• Topic: Medicine
• Subtopic: Anatomy

First published in 1881. The present work, on the structure and functions of the brain, is an abstract of the author's persoal experience as regards this subject. It is divided into two distinct parts; the first, anatomical, serves as the foundation of the work. It is followed by a second, purely physiological, which is its complement and necessary sequence. It includes chapters on the optic thalamus, the corpus striatum, and the memory in exercise.

Part I.
Anatomy of the Brain.

The Brain.

Chapter I.
Methods of Study.

The study of the nervous centres, has always strongly attracted the anatomist as a field of labour; and the reason of this is not far to seek. In the face of such a subject, not only does the very natural desire to penetrate the inmost secrets of the organization of the anatomical details under consideration come into play, but, further, there is that unconscious attraction which draws the human mind towards the unexplored regions of the unknown—towards those mysterious realms where the living forces of all our mental activities are silently elaborated, and where the solution of those eternal problems, regarding the relations of the physical organization of the living being to the acts of its psychic and intellectual life, evades us as we pursue it.

Hence it is that from century to century most of the great anatomists have, each in his turn, laboured in this direction. Hence Galen, Varolius, Willis, Malpighi, Vieussens, Vicq d'Azyr, Sommering, Reil, etc., have successively, in their immortal works, either described the organization of the nervous centres as they conceived of it at their own epoch, or expressed in their iconographies (with a more or less distinct glimpse of the truth) the objective fashion in which they saw the anatomical details they have successively represented.

In dealing with a subject so vast and so delicate, and a material so fragile and easily alterable as the nervous matter, the student is necessarily forced to depend on the different methods placed at his disposal by the arts and sciences of his own epoch. Hence the smallest technical discoveries frequently become of inestimable value; and it may be said, without exaggeration, that the utilization of chromic acid,* which, by hardening the nerve-substance, fixes it, with all its natural relations, without altering it, has been one of those new methods in laboratory work which have most essentially contributed to the success of those great achievements in this particular domain of anatomical science which our own century has witnessed.

* Hannover, in 1840, was the first to point out the hardening properties of chromic acid. (Robin, Traité du microscope, p. 297. J. B. Baillière, 1871.)

On the other hand, the perfecting of the magnifying power of microscopes has been of immense service, and has permitted the spirit of man to advance with vast strides into regions as yet unexplored, where it stands face to face with those ultimate anatomical units, the nerve-cells, of which our predecessors scarcely caught a glimpse. Thus it is now possible to give exact descriptions of their configuration, whether we study their connections, their minute structure, or the different pathological deviations they may undergo.

The introduction of the microscope into the study of histology has been in our century for the world of the infinitely little, what at another period of human development the intervention of the telescope was for the exploration of the sidereal world. It has rendered distinctly visible all those myriads of elements which, from their extreme smallness, were concealed from the eyes of our predecessors. It has brought them to light, revealed the secrets of their minute organization, and opened to the investigations of anatomists an entire new world of unexpected ideas.

Following upon this discovery, as a natural consequence, came the revelation of the art—previously unknown in our laboratories—of making thin slices of nervous tissue, colouring them, rendering them transparent, and preserving them. The employment of reagents of all kinds, which, testing in some degree the special sensibility of each histological element, colours it in a particular manner, and sets in relief the peculiarities of its structure, has opened a new road for progress; so that all over the civilized world, labourers, aided by physics and chemistry, have united their efforts, until we can say that the limits of the unknown recede, and that new conquests are perpetually being registered in our scientific reports.

But this is not all. In this kind of research it is not sufficient to see for ourselves the new facts met with on our road; it is necessary to make others see them, to represent in faithful statements the details of nature we have examined, and to. place the newly-registered facts beyond dispute.

Up to the present time it was the observer himself who pourtrayed, by means of his pencil, the objects which passed through the focus of his microscope. And, accordingly, we all know how widely these nominal drawings—even those made by masters of their profession—usually diverge from the truth; simply because they can never express more than those details which the artist has perceived and recognized, and a species of unconscious selection from the objects which are passing before his eyes. It is, then, in presence of these desiderata, as regards graphic representation, in drawings made by hand that we feel the necessity of applying the marvellous resources now offered us by photography to the reproduction of microscopic objects.

The sensitized plate henceforward plays its part in the world of scientific investigation, in the study of the phenomena that occur in the world of the infinitely little, as well as in the study of those that occur in the world of the infinitely great—registering histological facts as well as astronomical phenomena, and thus becoming the impersonal and automatic pourtrayer of the most minute details that have impressed themselves upon it Thus, wonderful to relate, photography, very much superior to drawing, not only reveals the objects which the eye perceives, but brings to light in addition a whole series of latent details, which await but the intervention of a simple lens to be successively recognized upon the prints when obtained.

These new means of investigation, which the scientine methods of the nineteenth century have placed within the reach of our generation, will, therefore, explain the progress accomplished, and show us once more that, in the long process of evolution which extends through ages, man only arrives step by step at the fragments of truth which he snatches, and that even his most persevering efforts only serve to cause the unknown to recede a few paces backwards. It is strange to find that, as fast as any progress is accomplished and new discoveries registered, new problems incessantly start up; and that just when we thought we had arrived at the utmost limits of the known world, at the demonstration of elements, simple, fixed, definite, our perfected methods of study enable us to see new complexities and unexpected horizons.

Thus, for instance, by means of high powers, the histological elements, of the nerve-cell, hitherto considered as the primordial and irreducible units of the system, become themselves divisible into secondary elements.

Photo-chemical histology, indeed, shows us that the protoplasm of the cell, formerly described as a homogeneous substance, is arranged in a fibrillary trellis-work; that its nucleus presents an arrangement of radiated fibres; and that what was thought to be the nucleolus is itself a complex element The nerve-cell thus becomes in its turn a little nervous organ sui generis. (See Fig. 2.)

The same analytic processes enable us, moreover, to demonstrate that the network, so dense and compact, which unites all the nerve-cells of the cerebral cortex, for instance, one with another, is so delicate that, when enlarged to 286 diameters, the fibres of which it is composed become visible, like single hairs in appearance and magnitude, etc.

What will be the end of these unforeseen details which present themselves in the train of each adaptation of a new method of study, to our researches into the nervous system?

No one knows as yet. It seems as though the secrets of nervous organization escape from our eyes as fast as we press further into the regions where they conceal themselves, and while anticipating the new methods of analysis which the future holds in reserve, we cannot help thinking that there is still much to do, and that now, more than ever, we should remember that true saying of Serres: " We have been dissecting the brain since Galen's time, yet there is not an anatomist who has not left his successors something to do."

The labours of which I am about to give a rêsumê are, then, but one of the phases of this long discussion concerning the structure of the nervous centres which has been going on for centuries.

If they do not establish the truth absolutely and finally, they will at least have the merit of being the result of contemporary science, and a sort of synthesis of the methods of work at our disposal.

The method I have employed for studying the organization of the cerebro-spinal centre in man, I have already explained in my first work.* It essentially consists in the preparation of a series of sections made methodically, millimetre by millimetre, vertically, horizontally, and antero-posteriorly; and—these sections being thus made according to the three dimensions of the solid mass which was to be studied—in reproducing them all photographically.

* J. Luys, " Recherches sur l'anatomie, la physiologie et la pathologie du système nerveux." Paris, 1865, J. B. Baiiliere.

I set myself, then, to make a series of successive horizontal sections of the brain, previously hardened in a chromic acid solution, from apex to base, at intervals of about one millimetre, and as perfect as possible; each being in its turn reproduced by photography.

I made similar sections of the brain in a vertical and antero-posterior direction, and at regular intervals from behind forwards.

These operations having been thus regularly conducted, this method enabled me to have representations of the reality as exact as possible; to keep the natural relations of the most delicate portions of the nervous centres each by each, according to their normal connections, and, in fact, without deranging anything. Thus by comparing the sections, horizontal or vertical, one with another, I could follow a given order of nerve-fibres in its progress, see its point of origin, and its point of termination; study the natural increase in complexity of the different kinds of nerve fibrils, millimetre by millimetre, changing nothing, lacerating nothing, and leaving everything pretty much in its normal position.*

* The plan of this work does not permit me to insist upon the innumerable difficulties I have surmounted, in arriving at the clear result already recorded in my photographic iconography. (Luys, "Iconographie des centres nerveux," J. B. Baillière, Paris, 1872,)

In the first place I had to invent cutting instruments sufficiently delicate to make complete sections of the brain, of the thickness of about one millimetre. But these pieces, when sufficiently hardened to undergo the action of the cutting instrument, had acquired, on coming out of the bath of chromic acid, that peculiar uniform greenish colouring -which renders them completely unfit for photogenic action. It was therefore necessary to discover a perfectly novel series of processes, in order to purify these sections from the chromic acid, and, without altering them, to impart to them photogenic properties. (See Journal d'Anatomic de Robin, Paris, 1872, for the whole series of the processes employed to bleach the sections tinted with chromic acid.)

By means of these new photographic methods of reproduction, which are all the more precise because impersonal, I had only, then, to register the details the sun himself had printed, to place the prints in juxtaposition, to compare them one with another, and thus to make a single synthesis of the multiple elements of analysis I had thus obtained by the automatic co-operation of the light.

The general view of cerebral topography having thus been fixed by these processes, the regions of more delicate texture, the special points which it was necessary to study in their minute elements, were further sufficiently magnified and reproduced, with successively increasing powers. I could thus render visible to the naked eye, and exhibit on a plan, details of structure which, up to that time, had only been seen in isolation under the tube of the microscope. By this means the mind of the observer, penetrating successively from the known to the unknown, from well-defined regions to those which are not so as yet, can easily make itself familiar with the details of the minute structure of the final nerve elements.

The cerebrospinal system in man ana the vertebrates consists of three departments, independent one of another, and yet very intimately connected. These are:—

I. The cerebrum proper.

2. The cerebellum and the apparatuses of cerebellar innervation annexed thereto.

3. The medulla spinalis and its encephalic expansions.

In this study we shall occupy ourselves with the cerebrum proper only.

The cerebrum consists of two lobes or hemispheres united to one another by a series of white transverse fibres, which form an anastomosis between the homologous regions of each lobe, so as to constitute a twin system, of which all the molecules are consonant one with another.

Each cerebral lobe, taken alone, presents for consideration in its turn:—

I. Masses of grey matter.

2. Agglomerations of white fibres.

The masses of grey matter, which are composed of many myriads of cells, and are the essentially active regions of the system, are arranged at the periphery in the form of a thin, undulating, continuous layer, which constitutes the cerebral cortex; and in the central regions in the form of two grey ganglions, coupled together, which are simply the grey substance of the optic thalami and corpora striata (opto-striate ganglions).

The white substance, essentially composed of nerve-tubules in juxtaposition, occupies the spaces comprised between the cortical periphery and the central ganglions.

The fibres of which it consists, and which merely represent lines of union between such and such regions of the cortical periphery and such and such regions of the central ganglions, run, like a series of electric wires stretched between two stations, in two principal directions.

I. Some directly unite the different points of the cortical periphery with the central ganglions, and are lost in their mass.

These are like the spokes of a wheel which unit...

Table of contents

• Cover
• Half Title
• Title
• Copyright
• Series Title
• Original Title
• Original Copyright
• PREFACE
• Contents
• PART I. ANATOMY OF THE BRAIN.
• PART II. GENERAL PROPERTIES OF THE NERVOUS ELEMENTS
• PART III. EVOLUTION OF THE PROCESSES OF CEREBRAL ACTIVITY