GANGLION CELLS OF THE CRAYFISH 197 



after a much longer interval of time. Kleist ('04) used in his experi- 

 ments half-grown cats and rabbits and found degeneration of the 

 spinal ganglion cells of the upper cervical and lower thoracic 

 nerves which had been severed. He further described some of 

 the cells which did not degenerate as having undergone distinct 

 atrophy, while others, he concluded, returned to a normal condi- 

 tion, since he found more cells at the end of four months than were 

 seen at the end of ten days. Van Gehuchten ('03) found degenera- 

 tion taking place centrally and declared it to be a true degenera- 

 tion, i.e., the same as that which takes place peripherally. He 

 also pointed out the importance of this process in tracing the 

 course of nerves. 



Ranson ('06) operated on white rats by cutting the second cer- 

 vical nerve and found simple atrophy and true degeneration in 

 the ventral and dorsal roots, the spinal nerve ganglia, and the 

 spinal cord. An apparently variable number of ventral-horn 

 cells disappear as a result of degeneration, likewise a considerable 

 and constant number of spinal ganglion cells. To avoid septic 

 infection of the parts studied, Ranson used methods which should 

 satisfy every requirement. 



It is seen that in a majority of cases changes are said to occur 

 in the central parts of the nervous system after nerves have been 

 severed. These changes consist in a reduction in the size of the 

 fibers and the ganglia, and, in fewer cases, in the disappearance 

 of the nerve fibers and nerve cells. Perhaps the mos,t convincing- 

 evidence of the disappearance of the ganglion cells is that found 

 in the results of Ranson in the disappearance of one-half of the 

 nerve cells in the spinal ganglion after cutting the second cervical 

 nerve in the white rat. 



EXPERIMENTAL ON THE FIFTH ABDOMINAL GANGLION OF THE 



CRAYFISH 



Retzius ('90) long ago described the structure of the abdominal 

 ganglia of Astacus fluviatalis. His work renders unnecessary a 

 complete description of these ganglia in Cambarus, the form used 



THE JOURNAL OF COMPARATIVE NEUROLOGY AND PSYCHOLOGY, VOL. 20, NO. 3. 



