GANGLION CELLS OF THE CRAYFISH 205 



the cells were less clearly denned, and the normal concentric 

 arrangement of the parts about the nucleus was more or less 

 disturbed. Usually in twelve to fourteen days after the operation 

 these changes became very evident. At this stage the fibrillae 

 had become more nodular and tortuous in appearance and the 

 axis-cylinder area was usually lost in the increased disturbance 

 in the arrangement of the cytoplasm of the cells. In addition to 

 these alterations in the organization, a marked change was seen 

 in the results of the action of the vom Rath fluid on the various 

 parts of the cells, in that they did not become black, as in the case 

 of normal cells, but assumed a somewhat yellowish color, instead. 

 This chromatolysis is one of the most characteristic alterations 

 observed in these cells and indicates chemical changes in their 

 constitution. This appeared early and increased as degeneration 

 advanced. This change is undoubtedly the chromatolysis demon- 

 strated by the Nissl method and observed in the spinal-ganglion 

 cells of dogs by Lugaro ('87), and in cats, dogs and rabbits by 

 Koster ('03). In eighteen to twenty days the fibrillae and axis 

 cylinder usually had entirely disappeared (figs. 5, 6), and the con- 

 centric arrangement about the nucleus had entirely broken up. 

 The flake-like bodies in the cytoplasm had given place to fine 

 granules. The nucleus (fig. 6) was usually collapsed and the 

 nucleolus had also undergone chromatolysis. The later stages 

 (fig. 7) , which were usually found at eighteen to thirty days after 

 the operation, were marked by the gradual loss of the various parts 

 of the cell. The fine granules visible earlier in the cytoplasm 

 disappeared, the nucleoplasm shrank, and the nuclear membrane 

 disintegrated. The nucleolus remained slightly longer than the 

 other organs of the cell and was seen sometimes to disintegrate 

 (fig. 8) and sometimes to grow fainter and fainter until it became 

 invisible (fig. 9). The order of these events rarely varied. 



The number of cells in the fifth ganglia which were affected 

 varied in different cases. This depended in part on the time that 

 had elapsed since the operation, and no doubt in part on slightly 

 varying conditions of the state of the animal. In no case did all 

 the ganglion cells in any ganglion disappear, and in no case did 

 degeneration fail to occur in a considerable number of cells within 



