412 M. J. GREENMAN 
It is seen that the probable error of the determination is more 
than one-half the difference found between the stimulated and 
the control fibers. Assuming that the areas of the largest fibers 
in the nerves of the right and left sides are similar under 
normal conditions then the difference should be more than three 
times the probable error in order to be significant. 
On further analysis of the data presented in table 4 it is found 
that when the first six entries are separately considered the aver- 
age sectional area of the right peroneal fibers is 7.8 square micra 
less than that of the left, while in the last six entries the average 
sectional area of the right peroneal fibers is only 1.6 square micra 
less than that of the left. 
Furthermore, in considering the entire group, if No. 363, which 
presents the greatest deviation from the mean, is omitted, the 
average sectional area of the right peroneal fibers becomes 96.0 
instead of 93.7 and the average sectional area of the left perme 
fibers becomes 98.8 instead of 98.4. 
The right peroneal fibers thus average 2.8 square micra 1n- 
stead of 4.7 square micra less in sectional area than the left. 
Assuming that the largest fibers of the right and left peroneal 
nerves are normally similar in sectional area, it would therefore 
seem that the slight difference in average sectional area noted 
between the right and left peroneal fibers was not due to the 
electrical stimulation of the right peroneal fibers, but that this 
difference is a deviation coming within the limits of normal 
variation. 
The axis sheath relation in this series is nearly the same for 
both right and left nerves—about 48 per cent axis and 57 per 
cent sheath. 
In a previous paper (Greenman, 713) it was stated that the 
intact nerve of an operated animal contains fewer medullated 
fibers than the same nerve from a normal animal of the same age, 
and that there is a loss in sectional area of fibers of the intact 
nerve of an operated animal. 
From table 4 it will be seen that normal inbred albino rats, 
of an average age of 153 days, have an average of 2070 fibers in 
