134 journal of Comparative Neurology and Psyshology. 



chromatic granules is concerned. The descriptions of Lugaro give 

 an idea of some of the various pictures that may be presented. 



ClIROMATOLYSIS. 



A general review of the literature on chromatoljsis would have 

 but little value for us. The observations of the previous investi- 

 gators will be discussed in connection with the particular problems 

 as these are taken up. It will, however, be necessary to present at 

 this point the procedure adopted in the more important investiga- 

 tions, as a basis for the comparison of results in the subsequent 

 pages. Lugaro ('96) cut the sciatic nerve in dogs at the level of 

 the hip joint, and also resected the brachial plexus in both dogs 

 and rabbits. The animals were allowed to live for periods varying 

 form 2 to 240 days. Cox ('98) resected the brachial plexus in 

 rabbits and allowed them to live for a period varying from one day 

 to a year. Cassirer ('99) removed a piece of the sciatic nerve at 

 the point of its exit from the pelvis, in rabbits which he killed 

 5 to 63 days after the operation. Koster ('03) also resected the 

 sciatic nerve immediately after its exit from the pelvis in cats, dogs, 

 and rabbits. The animals lived from a iew days to a year after 

 the operation. All these investigators prepared the spinal ganglia 

 associated with the injured nerves by some modification of Nissl's 

 method, most often staining with tolui din-blue. By the study of 

 ganglia removed at different periods after the operation they have 

 been able to follow the changes in the ganglion cells through the 

 various phases of chromatolysis. The following general statement 

 concerning these various phases is necessary as a preface to a dis- 

 cussion of the problems which each presents. 



Somewhere from 1 to 4 days after a nerve has been divided 

 changes become noticeable in the cells of the associated spinal 

 ganglion. There occurs a progressive solution of the tigroid sub- 

 stance beginning either near the nucleus or at a point intermediate 

 between the nucleus and the periphery of the cell. The cell becomes 

 swollen and the nucleus more or less displaced toward the periphery. 

 These changes characterize what will be called the ])hase of reaction. 

 After a time which varies within wide limits according to the con- 



