142 ^Journal of Comparative Neurology and Psychology. 



one would be justified in expecting to find a considerable number 

 of unaltered cells in this region of the ganglion. It does not seem 

 probable that such a condition could have been overlooked by all 

 those who have studied chromatolysis in the sjunal ganglion after 

 section of the peripheral nerve; and, having Bumm's observation 

 in mind, I have again gone carefully through my preparations, 

 but have been unable to see that this dorso-proximal region of the 

 ganglion showed any greater number of unaltered cells than are to 

 be found in any other part of the ganglion. This fact argues strongly 

 against the assumption of Bumm and Kleist that the dorso-proximal 

 part of the ganglion is the locus of cells which send a fiber into 

 the dorsal root but none into the nerve. Just why the cells in 

 the dorso-proximal part of the ganglion should be more susceptible 

 to a lesion of the dorsal roots than the other cells of the ganglion 

 is hard to say. It should, however, be borne in mind that it is just 

 this portion of the ganglion that woidd be most ex])osed to direct 

 trauma in an operation on the dorsal roots, and that it would 

 also be most affected by any anaemia produced by the division 

 of the arteriole accompanying the dorsal root. It is not probable, 

 however, that these are determining factors, and the observations 

 of Bumm and Kleist may still have an important but as yet unde- 

 termined significance. 



It has been shown that there is no special area which is most 

 affected, but there still remains the question whether any particular 

 type of cell is more susceptible than another. One of the clearest 

 observations that can be made on the material from the white rat, 

 is that the cells which disappear belong for the most part to the 

 small cell type. It is true that it is very difficult to follow the 

 different steps in the disintegration of these cells, and it would be 

 impossible to reach this conclusion by direct observation of the process 

 of degeneration. The only hint in this direction which such a study 

 gives is the fact that the nuclei of these cells are much more excentric 

 than those of the large cells, so much so that the nucleus often 

 appears as a second sphere attached to one side of the cell body. 

 It is clear, however, that as the length of the post-operative period 

 increases, the number of cells diminishes, spaces are left filled with 



