2 20 fouiiial of Comparative Neurology and Psyehology. 



of the entire number. We have already stated that the author's 

 enumeration of the nerve fibers in the ventral roots of the left 

 spinal nerve is 26.83% greater than the estimate made by 

 Stilling. And we have also shown that Stilling failed to in- 

 include in his estimate the nerve fibers the diameter of which 

 is less than 7. 5 //. It therefore seems probable that these small 

 fibers would account for the difference (26.83%) between the 

 author's enumeration and Stilling's estimate. Were this ex- 

 actly the case, the small fibers should amount to about 26.83% 

 of the entire number in the ventral roots. But we have found 

 that the calculation made above places the small fibers at 39. 64 % . 

 It therefore becomes necessary to search for the cause of this 

 discrepancy. The above reasoning, (i. e., that the percentage 

 of small fibers should exactly account for the difference) is valid 

 only on the assumption that the number of large fibers was 

 similar in the two cases compared. We must therefore deter- 

 mine whether or not the ventral roots used by Stilling proba- 

 bly contained the same number of large fibers as the ventral 

 roots used by the author. To simplify this matter we shall 

 again compare the areas of the ventral and dorsal roots of the 

 left spinal nerves, as determined by Stilling and by the author. 



Total area of ventral Total area of dorsal Ratio 



roots roots 

 Stilling 



(female) 35.23 mm.-' 57.95 mm. 2 1:1.64 

 Author 



(male) 26.50 " 54.93 " 1:2.07 



We have already suggested that the ventral roots in Still- 

 ing's case were larger than we should expect and the table 

 above illustrates this point. Taking the areas of the dorsal 

 roots as standards and assuming our own area for the ventral 

 roots to be correct, then the following proportion (54.93 : 

 57.95 : : 26.50 : x) gives 27.96 mm.- as the area to be antici- 

 pated for the ventral roots in Stilling's case. From this it is 

 evident that if we could assume the same ratio to exist between 

 the ventral and dorsal roots in males and females, the area of 

 the ventral roots in Stilling's case should be 27.96 mm.'- in- 

 stead of 35.23 mm.'-. We have here, probably, the reason for 

 the discrepancy between the number of fibers by which the 



