INGBERT, Dorsal Roots of Spinal Nerves. 69 
order to determine, roughly, this relation between the large and 
small fibers | have counted all the nerve fibers the diameter of 
which is more than 7y in the dorsal roots of C.II and Th. VII 
of the spinal nerves of the left side. According to this count 
the dorsal root of C.II contains 12,621, and that of Th. VII 
4,621 of these large fibers. From Table I¢ it is seen that the 
former contains in all 28,375, and the latter 12,325 nerve fibers. 
Calculations based on these data indicate that in the dorsal root 
of C. II 55.5% of the fibers are ess than 7y, and in the dorsal 
root of Th. VII, 62.4%. 
We therefore conclude from the calculations based on the 
results of StTiLLinG and on my own results, that 55 to 60% of 
the fibers in the dorsal roots of the spinal nerves are less than 
7 in diameter, i. e., having a smaller diameter than the small- 
est nerve fiber measured by Stitiinc._ The failure on the part 
of STILLING to include the fibers the diameters of which are 
less than 7 is no doubt the chief source of the difference be- 
tween STILLING’s results and my own. 
V. The Number of Nerve Fibers per Square Millimeter of the 
Cross-Section of the Dorsal Roots of the Spinal Nerves of 
Man. 
According to the data which we have taken from STILLING 
the dorsal roots of the spinal nerves in man have an area on the 
left side of 57.95 mm.” and contain 262,gI9 nerve fibers, or in 
other words, they contain 4,537 nerve fibers per sq. mm. of 
the cross-section. 
According to my results, the dorsal roots in the case ex- 
amined have on the left side an area of 54.93 mm.’, and con- 
tain 653,385 nerve fibers, or on the average, I1,gOI nerve 
fibers per sq. mm. of the cross-sections of the roots. 
This comparison is but another way of showing that SriLt- 
ING failed to observe the small fibers. 
In my projections of the dorsal roots of the left side, as 
well as in the tables accompanying them, are found the relative 
number of nerve fibers for each fascicle, expressed in thousands 
persq. mm. From a study of these it is evident that the rela- 
