PROGRESS IN EXPERIMENTAL PSYCHOLOGY 



microscopical methods, most important aid is given by 

 a method originated by Waller in 1852. Earlier than 

 that, in 1839, Nasse had discovered that a severed nerve 

 cord degenerates in its peripheral portions. Waller dis- 

 covered that every nerve fibre, sensory or motor, has a 

 nerve cell to or from which it leads, which 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 cen- 

 tres, 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 between a nervous 

 tract and its trophic centre, sharply defined tracts could 

 be made to degenerate, and their location could subse- 

 quently be accurately defined, as the degenerated tis- 

 sues take on a changed aspect, both to macroscopical 

 and microscopical observation. Recognition of this 

 principle thus gave the experimenter a new weapon of 

 great efficiency in tracing nervous connections. More- 

 over, the same principle has wide application in case of 

 the human subject in disease, such as the lesion of nerve 

 tracts or the destruction of centres by localized tumors, 

 by embolisms, or by traumatisms. 



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 strength- 

 ened by experiments of the students of motor localiza- 

 tion, which showed that the veritable centres of their 



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