no Journal of Comparative Neurology. 



In most cases we can determine without any trouble 

 whether in successive sections we are deaHng with two parts of 

 the same cells or different cells, and thus the actual error intro- 

 duced in this way is probably very small. The determination 

 of the small and large cells was made according to the method 

 used in my previous paper on the spinal ganglion cells (1901, 

 I). The class of intermediate cells recognized in that paper 

 was neglected in this study, these cells being classified as large 

 or small according to their diameters. At first, the entire num- 

 ber of the cell-bodies including both large and small, was enum- 

 erated. Then the large cells alone were enumerated and their 

 number was deducted from the total, thus giving the number 

 of small cells. 



III. On the Spinal Ganglion Cells.- 

 A. Total Number of the Spinal Ganglion Cells at Different 

 Ages. 



The number of the nerve cells in the spinal ganglia has 

 been determined by several investigators : 



Freud ('78), in the spinal ganglia of Petromyzon ; Hodge 

 ('88) in the spinal ganglia of the frog ; Gaule and Lewin ('96) 

 in the spinal ganglion of the rabbit ; and Buhler ('98) in the 

 spinal ganglion of the frog. So far as I am aware, no investi- 

 gators have ever enumerated the number of the spinal ganglion 

 cells at different ages in the same animal. 



The following table shows the total number of the spinal 

 ganglion cells in the three ganglia at different ages : 



TABLE I. 



Total Number of Cells in the Spinal Ganglia of Male White Rats 



at Different Ages. 



Body Weight 



Grams. VI CervicaL IV Thoracic. II Lumbar. 



Average number 11140 73o6 8867 



' These figures were obtained from a rat having a body-weight of 69 grams 

 and not from the one weighing 68.5 grams, the cervical ganglion of which wai 

 alone counted. 



