GANGLION CELLS OF THE CRAYFISH 207 



The nerves showed a more advanced state of degeneration at and 

 near the cut surfaces than was found at points more remote from 

 these surfaces. 



DISCUSSION 



It has been found in the experiments described in this paper 

 that the ganglion cells in the fourth, fifth and sixth abdominal 

 ganglia of Cambarus bartonii undergo distinct structural changes 

 when the connectives and lateral nerves are severed. A larger 

 number of cells is affected in the fifth ganglion than in the others ; 

 this ganglion, from the nature of the operation, had more of its 

 nerve fibers cut than either of the other two. That these changes 

 were due to the cutting of the nerve is beyond reasonable doubt , 

 since they were found only in those ganglia which had their 

 connectives severed, and were found in every such case. That the 

 changes are those connected with true degeneration finds support 

 in the fact that they resemble in their essen t ial points the histological 

 changes in the corresponding parts of the nerve fibers and cells 

 of vertebrated animals as described by Monkeberg und Bethe 

 ('99), Kleist ('04), and others. In all cases chromatolysis is 

 reported to have occurred soon after the nerves were severed, 

 which indicates important chemical changes in the nerve cells. 

 Following this were characteristic alterations of the nerve 

 fibrillae and other structures of the cell, resulting finally in 

 the 'destruction of the cell itself. Kleist ('04) stated that two 

 to six days after the sciatic nerve in dogs, cats and rabbits had 

 been severed, alterations occurred in the tigroid bodies of the spi- 

 nal ganglion cells. In ten days vacuolar degeneration and shrink- 

 ing of the cells had occurred. It has been shown in this paper that 

 alterations in the tigroid bodies of the ganglion cells of Cambarus 

 were found five to seven days after the connectives had been cut, 

 and that in ten to twelve days the fibrillae were distinctly altered 

 and a shrinking of the cytoplasm and nucleus had occurred. 



In regard to the time required for complete degeneration to take 

 place, experimental results vary widely. Fleming ('97) observed 

 disintegrating nerve cells in six weeks, but many more in eighteen 

 weeks. Koster ('03) found that only relatively few cells had de- 



