ANATOMY OF THE BRAIN.
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 pene trate the inmost secrets of the organization of the anato mical 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 organi zation 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 immortal works, either described the organization of the nervous centres as they conceived of it at their own epoch, or expressed in their icono graphics (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.
On the other hand, the perfecting of the magni fying 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 conse quence, came the revelation of the art—previously un known in our laboratories—of making thin slices of nervous tissue, colouring them, rendering them trans parent, 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 pecu liarities 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.