HISTORY AND METHODS OF INVESTIGATING. 5 



and the spinal cord, in a scries of masterly works, showing an 

 industry never surpassed, and which will surely remain forever a 

 monumentum cere perennius of the great physician of Cassel. 



Meynert, however, not only examined carefully and system- 

 atically every region of the brain and spinal cord, both by 

 sections and by teasing, but by these means he made more new 

 discoveries than had been made by any previous investigator 

 with the exception of Stilling. He not only did these things, 

 but, with the inspiration of true genius, he set up a theory of 

 the structure of the brain, based on its finer anatomy, which 

 still exerts an influence on the anatomy and psychology of 

 to-day, and spurs us on to further discoveries. 



It follows, from the very nature of Stilling's method, that the 

 course of a nerve-tract can only be traced with certainty so long 

 as the component fibres are not interrupted by ganglion-cells, 

 do not pass out of the plane of the section, do not enter a 

 plexus of fibres, or split up into innumerable fibrils to be dis- 

 distributed in every direction. Even in the spinal cord of the 

 smallest animal it rarely occurs that a nerve-fibre can be observed 

 running its whole course in the plane of one section. It is, on 

 the contrary, the rule of the central nervous system that the 

 nerve-tracts from periphery to centre are broken up by interpo- 

 lated ganglion-cells, and rendered difficult to follow by the 

 frequent interchange of fibres. 



Efforts were made, therefore, particularly after we had 

 beo-un to learn something in this difficult field from the works 



o o 



of Stilling, to devise further methods which would enable us to 

 discover and locate the nerve-tracts. It is known that Waller, 

 in 1852, showed that divided nerves degenerate in definite 

 directions. Before this (1850), Turk had found that a break in 

 the conductivity of the spinal cord led to degenerations which 

 spread upward in different columns from those affected by the 

 descending degenerations. By his labors, and those of Bou- 

 chard, Flechsig, Charcot, Monakow, and many others, it was 

 ascertained that perfectly definite sets of fibres always occupy 



