112 'Journal of Comparative Neurology and Psychology. 



a normal dorsal root associated with a ganglion which has lost one- 

 half of its cells, is susceptible of another explanation than that 

 suggested by Nissl's theory. All in all, then, while the evidence 

 requires that we should be open-minded on this question, it is 

 not sufficient to overthrow the belief that the dorsal roots are pre- 

 dominately composed of the central branches of Ranvier's T- 

 processes. The evidence from the silver preparations, that one 

 branch of the stem process of the spinal ganglion cell runs through 

 the dorsal root, is very convincing. This evidence has been well 

 summarized by van Gehuchten ('92). 



2. Numerical relations between the spinal ganglion cells and 

 the medullated fibers of the dorsal roots. — Freud ('78), working on 

 Petromyzon, found a considerable excess of fibers in the dorsal 

 roots over the cells in the spinal ganglion, due to the fact that the 

 cell bodies of many of the afferent neurones are located in the 

 spinal cord. Hodge ('89) counted the dorsal root fibers and the 

 cells in the associated ganglion in the frog, and found about three 

 cells for each fiber. Buhler ('98) has shown that the number of 

 cells in the spinal ganglia increases as the test-animal is higher in 

 the zoological series; least for fish, it is greatest in mammals. He 

 also found that in the frog there were about five ganglion cells for 

 each dorsal root fiber. Gaule and Lewin ('96) found in the 

 rabbit a ratio between cells and fibers of 6 to i. Hardesty ('05) 

 found in the frog a ratio varying from 2.7 to 3.6 cells per fiber. 

 Hatai ('02), working on the white rat, obtained the following 

 results for the adult specimen of 167 grms. body weight. 



TABLE II. 

 Ratio of Spinal Ganglion Cells to Dorsal Root Fibers (Hatai). 



Nerve. Number of Cells. Number of Fibers. Ratio. 



VIC t2,200 4.227 1:2.8* 



IV T 4,406 1,522 1:4.8* 



IIL 9,442 1,644 1:5-7 



* The figures 2.7 and 4.3 given in the original are obviously misprints. 



The writer, in studying the normal relations in the second cerv- 

 ical nerve of the white rat, has obtained results confirmatory of 

 those of the authors already mentioned. In the three cases in 

 which the dorsal root fibers and spinal ganglion cells were enu- 



