b AKTATOMY OP THE CENTEAL NBEVOUS SYSTEM. 



are certain to make for the great Cassel physician a monumentum (Bn 

 perennius. 



Meynert, however, not only systematically worked through the whole 

 field of brain- and cord- anatomy, discovering, through sections and dis- 

 sections, more new facts than had any preTious investigator. Stilling ex- 

 cepted; but, upon minute anatomy as a basis, he formulated a theory of 

 brain-structure which has equally influenced anatomy and psychology, bear- 

 ing fruit up to the present time and stimulating investigators to new 

 discoveries. 



Prom the nature of the Stilling method it follows that the tracing of 

 a nerve-tract for considerable distances is made certain only so long as the 

 elements which combine to form it are not interrupted by ganglion-cells 

 or turn out of the plane of the section, so long as it does not pass into a 

 fiber mesh-work or from one bundle split up into numerous diverged 

 fibrillae. Even in the spinal cord of the smallest animals it seldom occurs 

 that the entire course of a fiber may be seen in the plane of one section. 



It was, therefore, necessary, after getting one's bearings in this dif&cult 

 field through Stilling's work, to seek for further methods which would per- 

 mit the finding and tracing of nerve-tracts. 



As is well known, Waller (1852) showed that severed nerves de- 

 generate in a definite direction. Tiirck had already shown (1850) that even 

 the interruption of conduction in the spinal cord leads to degeneration, 

 which progresses upward in some tracts and downward in others. 



Through his studies, as well as through those of Bouchard, Flechsig, 

 Charcot, et al, it was successfully demonstrated that in definite tracts of 

 the spinal cord and the brain lie fibers which, when degenerated, separate 

 themselves from the normal tissues along their entire course, and may 

 thus be easily followed. The study of these secondary degenerations has 

 since become important for the advance of the science with which we 

 are employed. For this reason let us for a moment discuss Waller's law 

 somewhat more in detail. 



It is now formulated as follows: The axis-cylinder of a nerve-fiber 

 remains intact only so long as it is in connection ivith its parent-cell. It 

 degenerates along with its sheath beyond the point where its connection 

 with the parent-cell is severed. But Forel has shown that, in the newborn 

 after simple severing of the nerve and in adults if the nerve is divided 

 very near to the nucleus (ganglion-cell), degeneration may occur also in 

 the nerve-segment which is connected with the cell. Bregmann has also in 

 an investigation especially planned with this point in view, confirmed the 

 theory of the degeneration of the central stump. This apparent contra- 

 diction of AValler's law has been solved by the studies of iS^ssl. Nissl has 

 shown that a harmful influence is exerted upon the central cell from the 



