InGBERT, Dorsal Roots of Spinal Nerves. 63: 
only one attémpt at a determination of this kind, viz., that of 
STILLING. 
zr. Stiling’s Estimate. The material used by STILLING 
(1859)” for this work was the same as that employed in mea- 
suring the areas. In this investigation he made use of a com- 
pound microscope in the oculus of which was placed an ocular 
micrometer on which was a square 3’” (Paris lines) on each 
side, and each side again was divided into 120 parts by parallel 
rulings. | He counted in a certain number of the small squares 
thus formed the number of cross-sectioned nerve fibers seen 
within them, and from this estimated the number for the entire 
square. This he found to be from 120-176, average 148, for 
the dorsal roots. He does not state what roots he examined 
nor how many counts were made. Since the magnification 
used was 37.5 diametérs or 1406 in area, the amount of the 
section seen within the square would be g-1406 or I-156 of a 
square line. If 1-156 of a square line of the section contains 
148 fibers, one square line will contain 156X148, or 23,088 
fibers, which is equal to 4,537 fibers for each sq. mm. Since 
in his case there were 57.95 mm.” in the area of the dorsal 
roots of the 31 left spinal nerves, there will be 57.95 X4,537, or 
262,919 nerve fibers in all of them. And since the right dorsal 
roots have an area of 55.09 ram.”, they will have 55.09 4,537, 
or 249,943 nerve fibers, and the dorsal roots of both sides 
5 12, 862. 
STILLING’s estimate for the number of nerve fibers in the 
dorsal roots of both sides is, however, not 512,862, but 504,- 
473. This difference is due to the fact that he based his esti- 
mate on the area of the dorsal roots as obtained by his method 
of weighing, which gave 111.23 mm.” for both sides, and the 
calculations I have made are based on his areas as obtained by 
the planimeter, which gives 113.04 mm.” The latter areas 
were selected because they may be more properly compared 
with my own, which were also obtained by planimetric mea- 
surements. 
2. Author's Enumeration. In making the enumeration of 
the number of nerve fibers in the dorsal roots of the left spinal 
