284 'Journal of Comparative Neurology and Psychology. 



months. According to our present knowledge there is no reason 

 to expect any regeneration of the spinal ganglion cells. This state- 

 ment is based in part on Hatai's ('02) study of the growth changes 

 in the spinal ganglia, but more particularly on the negative results 

 of a series ol investigations undertaken for the purpose of testing 

 the regenerative capacity at one time supposed to belong to these 

 structures (Tirelli '95, Monti and Fieschi '95). The slight 

 excess of cells in the four-month specimens is probably of no sig- 

 nificance, representing nothing more than the individual variation 

 of which so much has already been said. Further support is given 

 to this view by the fact that of the two specimens enumerated the 

 first gives a figure close to the average for the two-month specimens 

 while the second runs much higher and in all probabilty represents 

 a large ganglion which originally contained over 9000 cells. 



The point of importance is not that there is a slight excess of 

 cells in the four-month specimens, but that there is certainly no 

 decrease, and that, therefore, the process of cell-destruction runs a 

 rather rapid course and is completed during the first two months, 

 after which there is no further change. This is of interest in con- 

 nection with the usual doctrine that in chromatolysis the phase 

 of reaction is followed by a phase of restitution, which may result 

 in the complete restoration of the cell, or may in turn give place 

 to a phase of degeneration, resulting in the gradual disappearance 

 of the injured neurones. It is obvious that in this case the phase 

 of degeneration (if it can properly be separated as a distinct phase 

 at all) must have been a rapid one which came to a definite ter- 

 mination. It did not result in the destruction of cell after cell until 

 all had disappeared. According to recent observations of Koster 

 ('03), who cut the sciatic nerve in cats, rabbits and dogs, the cell 

 destruction in the spinal ganglia is only slightly noticeable after 

 100 days, but is very marked after 284 days. There can be no 

 doubt that in my experiments on rats the degeneration was com- 

 plete before the end of the first sixty days. That my animals 

 were very young and of a different zoological order from those of 

 Koster, may in part explain the discrepancy in the results. It 

 should be mentioned, however, that Koster did not control his 

 observations by an actual enumeration of the cells. 



By reference to Table IX it will be seen further that the number 

 of ventral root fibers is greater in the animals which survived four 

 months than in those which were killed at an earlier date. The 



