NERVOUS SYSTEM AND BRAIN. tits Toatwo,. It is impossible in an article such as the present to do more than touch upon sonic of the more important investigations which have brought us to our present conception of nervous system structure. To the philosopher Descartes, in the latter part of the sixteenth century. be longs the honor of the first recorded description which gives any intelligent conception of the structure of the nervous system. Bis drawings of the brain possess a very fair degree of ac curacy as regards general shape, though the lobes and convolutions appear much distorted. Ile pictured the nerves as originating in the brain and described their function as the carrying of the 'animal spirits' from the brain to the periphery. For the next two hundred and fifty years little progress was made in the study of the structure of the nervous system, though some work was done upon the gross anatomy of the brain by men whose names remain to us in our anatomical nomenclature. Thus, Vesalins, Fab. lopius, and Eustachius were among the earliest. In the seventeenth century we have Willis, whose name we recognize in the circle of Willis, and who described the basal ganglia, the pyramids and the olives; Vieussens, whose name is famil iar in the valve of Vieussens; and Dnboise. whose medical cognomen of •Sylvius' marks that promi nent sulcus of the cerebrum. The results of the labors of these investigators, as well as of those of Van Leeuwenhoek, of Alalacarne, of Rolando. of Vico d'Azyr, of Arnold, of Monro, and others were collected and summed up in an extensive volume published by Burdaeh in 1819. Descartes had discovered the nerve fibre, and the next step forward in the histology of the nervous system was not taken until Ehrenberg in 1833 discov ered the nerve coil in the spinal ganglia. This discovery was emphasized when four years later Purkinje observed the presence of cells not only in the ganglia, but in the cerebrum and eery bellum. The important fact that the dorsal roots of the spinal nerves are concerned with sensation and the ventral roots with motion was discovered by Sir Charles 11411. an eminent
British surgeon and anatomist. and eommuni eated by him to the Royal Society of London about 1820. In 1834 Remak discovered that the cells of the sympathetie ganglia had processes, and that these processes were connected with nerve fibres. The import anee of this discovery, confirmed in 1842 by Helmholtz, was not at the time appreciated. One of the most careful stud ies of nerve cells and their processes was made by Otto Deiters of Bonn and published after the death by Sias in 1S65. Deiters divided the processes given from nerve cells into two kinds, protoplasmic esses, which branched rapidly and the structure of which resembled that of the cell body, and axis cylinder or nervcnis \Odell wwcre often l'011tillUOIIS \Vail the axis inders of inedullated nerves. tion in far-reaching in its intluence. I;y the use of the chloride of gold method, lie was able to demonstrate many more and Liner proc esses of nerve cells than had been revognized by the older methods of staining. These delicate processes %VerC believed by Gerlach to form a fuse nervous network within the gray matter.
its ides describing this nervous network, lach built up upon this as a basis a theory of nervous system structure which WaS CCept Pli by most 11111 the advent of the called 'newer Gerlach belhwed that from the anterior horn yells of the spinal cord, processes passed directly off to form the motor roots of the spinal nerves. According to his theory the protoplasmic processes of these cells ramified ill the gray matter of the cord, where they with protoplasmic /woe esses from other coils, forming a reticulum from whirl' arose the fibres Ivhieli passed out of the e-ird as the posterior or sensory roots. Gerlach lidieved that this same relation of afferent and fibres to the nerve cells and to the ngeoiIoW obtained t rOlIgh011t the entire nervous Which of a remarl:ably complex continition of nervous protoplasm.