Ingbert, Ventral Roots of Spinal Nci-ves. 221 



author's enumeration differs from Stilling's estimate (26.83%) 

 and the number of small fibers actually found (39.64%). 



To test this, another calculation becomes necessary. The 

 ventral roots of the left spinal nerves, according to Stilling, 

 have an area of 35.23 mm." and contain 149,058 nerve fibers. 

 If these ventral roots had an area of only 27.96 mm.-, their 

 area would be in the same ratio to the area of the dorsal roots 

 as are the areas in the author's case, and would contain (accord- 

 ing to Stilling's method of estimation) only 118,299 nerve 

 fibers. This is 58.07% of the author's estimation; or, in other 

 words, it is 41.93% less. But from our calculation above the 

 small fibers in the author's case constitute 39.64%, hence we 

 conclude that the difference between Stilling's estimate of the 

 number of nerve fibers in the ventral roots and the author's 

 enumeration is accounted for within 2 % by the small fibers 

 which Stilling omitted. It does not seem probable that this 

 increased area in the ventral roots in Stilling's case was due to 

 large masses of connective tissue for he was on his guard against 

 this source of error ; but a diffused increase might have been 

 present. 



Finally, the difference may be due to individual variation, 

 or may be due to difference in sex. This later possibility will 

 be considered further on. 



V. The Nnniber of A^en>e Fibers per Square Millimeter in the 

 Cross-Seetions of the Ventral Roots of the Left Spinal 

 Nen'es of Man. 



I. Determinations and Comparisons. — According to Still- 

 ing, the ventral roots of the left spinal nerves have an area in 

 cross-section of 35.23 mm." and contain 149,058 medullated 

 nerve fibers, or, in other words, they contain 4,231 nerve fibers 

 per sq. mm. of the cross-section. 



According to the author's results, the ventral roots of the 

 left spinal nerves have an area in cross-section of 26.50 mm.", 

 and contain 203,700 medullated nerve fibers, or, 7,687 nerve 

 fibers per sq. mm. of their cross-section. 



The difference between the number of nerve fibers sq. mm. 



