Hatai, Ganglion Cells in the Rat. 109 



For the counting and measurements of the cell-bodies, the 

 sections were cut 12 micra in thickness, while for the nerve 

 fibers 6 micra was found to be a convenient thickness. For the 

 enumeration of the nerve-fibers, the writer employed exclusively 

 the photographic method as used by Dr. Hardesty (1899) in 

 this laboratory ; since, by this method, the enumeration of the 

 nerve fibers is made most accurately and with least fatigue. 

 The countings of the nerve cells, however, was done with the 

 net under the microscope, using oc. 4 X obj. 8 mm. of Zeiss. 

 Since the large nerve cells (50 micra in diameter), as well as 

 the nuclei (16 micra in diameter) may appear in more than one 

 section, the count was made by enumerating the nucleoli. For- 

 tunately, the presence of multi-nucleoli is very rare in the large 

 cells, though it is not uncommon in the small or smallest cells. 

 Under these' conditions, an error in the counting would occur 

 only when one nucleolus was in one section and the other in a 

 second, an arrangement so rare that it may be neglected. 



In studying the numerical relations between the cells in 

 the spinal ganglion of several sacral nerves of the rabbit, and 

 the fibers in the corresponding dorsal nerve roots, Lewin (1896) 

 first counted the cells by enumerating the nucleoli as they ap- 

 peared in successive sections. This gave him such a large num- 

 ber of cells that he feared that an error had been introduced, 

 owing to the presence of double nucleoli. To correct this, he 

 made another enumeration of cells by the following method. He 

 counted the number of cells which appeared in all of the sec- 

 tions, each section being 10 micra in thickness, and then esti- 

 mated the average diameter of nerve cells by taking the mean 

 of largest and smallest there present. Employing this average 

 diameter, he then calculated the number of cells. This gave a 

 smaller number than that obtained by counting the nucleoli. 

 The error introduced, however, by employing the average diam- 

 eter, owing to the variable ratios of large and small cells in any 

 given ganglion, is much greater than that connected with the 

 first and simpler method. For this reason the direct enumera- 

 tion of the nucleoli, due care being taken to avoid counting 

 double nucleoli, has been used in this case. 



