GANGLION CELLS OF THE CRAYFISH 203 



cells in various stages of disintegration in the fourth, fifth and sixth 

 ganglia. This unmistakably demonstrated the usefulness of this 

 method for detecting degenerating cells. In the fourth ganglion, 

 certain large nerve cells were almost wholly disintegrated, while 

 adjoining nerve cells were apparently normal. This is considered 

 significant, since this ganglion had only the connective between it 

 and the fifth severed. A similar condition was found in the sixth 

 ganglion, which had only its anterior nerve connections severed. 

 The fifth ganglion showed more extensive changes, which will be 

 referred to later. 



By this method preparations were made of material in situ 

 at intervals of three or four days over a period of thirty-eight 

 days from the time of operation. Corresponding normal ganglia 

 were given treatment at the same time and mounted in parallel 

 series with the isolated ganglia in a majority of the experiments. 

 In later experiments parallel series were deemed unnecessary 

 because of uniformity in results. 



Were it not needed for comparison, it would be unnecessary to 

 give even a brief description of the normal ganglion cell prepared 

 according to the vom Rath method. The action of the fluid on the 

 nerve cells is such that the various cell structures are well differen- 

 tiated in black and white. The fibrillae (fig. 3) are very clearly 

 seen in the axis cylinder within the cell as very fine dark lines. 

 They are frequently also seen in the protoplasm of the cell sur- 

 rounding the nucleus. Numerous flake-like bodies, apparently 

 having some relation to the Nissl bodies, lie in the cytoplasm, 

 arranged concentrically around the nucleus. This concentric 

 arrangement of parts around the nucleus is a condition which will 

 be referred to in a future paragraph. The nucleus shows the charac- 

 teristic nuclear membrane, network, and nucleolus. 



In ganglia which had been isolated five to seven days, some 

 of the large ganglion cells had begun to show alterations in their 

 structure. The large cells in the posterior part of the ganglion were 

 among the first to become affected. Some of the smaller cells in 

 this part showed on-coming changes somewhat earlier. In the 

 large cells the fibrillae (fig. 4) became somewhat nodular and 

 tortuous in their course. The limits of the axis-cylinder area in 



