MYELINATED FIBERS——PERONEAL NERVE OF RAT 405 
areas of fibers, axis and sheath were determined by measuring with 
a compensating planimeter an outline of each fiber and of its con- 
tained axis, magnified 4000 diameters. These outlines were 
drawn on finely ground glass in the plate holder end of a specially 
constructed rigid camera. A Zeiss 2 mm. apochromatic objec- 
tive with No. 4 compensating ocular constituted the optic ap- 
paratus of the drawing camera. 
In order to keep the personal factor as low as possible all 
counts and all planimeter records were made by my assistant, 
while all drawings were made by myself. 
For the skillful technical work and the accuracy of the counts 
and planimeter determinations I am indebted to Miss F. Louise 
Duhring. 
Table 1 presents the summarized data of this preliminary 
test. 
TABLE 1 
eee AVERAGE SECTIONAL AREA OF 
NUMBER AT TIME OF NESE 20 LARGEST FIBERS 
Fiber Axis Sheath 
BOemO? (EXEreIsed)).- onsen. ee. 226 1996 84.1 35.3 48.8 
gee. (COMMOL)J +. 2.2204. 25.) 236 2054 105.6 40.3 | 65.2 
The control fibers average 20.4 per cent larger than the fibers 
of the exercised animal. 
The average axis-sheath relation in the control fibers is 38 
per cent axis to 62 per cent sheath, while the average axis-sheath 
relation in the exercised animal is 42 per cent axis to 58 per cent 
sheath, showing a very slight difference in the percentage of 
sheath. 
This preliminary test suggested that peripheral nerve fibers 
may be affected in area of section by excessive exercise and that 
possibly the axis-sheath relation may be thereby modified. 
However, as the animals were not known to be of the same litter, 
and as the limits of individual variation as to fiber areas were 
unknown, the test could only be regarded as an encouragement 
to pursue the work further. 
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 27, NO. 3 
