A HISTORY OF SCIENCE 



dominates its nutrition, so that it can only retain its 

 vitality while its connection with that cell is intact. 

 Such cells he named trophic centres. Certain cells of 

 the anterior part of the spinal cord, for example, are 

 the trophic centres of the spinal motor nerves. Other 

 trophic centres, governing nerve tracts in the spinal 

 cord itself, are in the various regions of the brain. It 

 occurred to Waller that by destroying such centres, 

 or by severing the connection at various regions be- 

 tween a nervous tract and its trophic centre, sharply 

 defined tracts could be made to degenerate, and their 

 location could subsequently be accurately defined, as 

 the degenerated tissues take on a changed aspect, both 

 to macroscopical and microscopical observation. Rec- 

 ognition of this principle thus gave the experimenter a 

 new weapon of great efficiency in tracing nervous con- 

 nections. Moreover, the same principle has wide ap- 

 plication in case of the human subject in disease, such 

 as the lesion of nerve tracts or the destruction of cen- 

 tres by localized tumors, by embolisms, or by trau- 

 matisms. 



All these various methods of anatomical examination 

 combine to make the conclusion almost unavoidable 

 that the central ganglion cells are the veritable " cen- 

 tres" of nervous activity to which so many other lines 

 of research have pointed. The conclusion was 

 strengthened by experiments of the students of motor 

 localization, which showed that the veritable centres 

 of their discovery lie, demonstrably, in the gray cortex 

 of the brain, not in the white matter. But the full 

 proof came from pathology. At the hands of a multi- 

 tude of observers it was shown that in certain well- 



280 



