416 M. J. GREENMAN 
nerve are within the limits of normal variation and that there 
is practical symmetry between the largest fibers of the right and 
left peroneal nerves. 
Further support of this conclusion is to be furnished by an 
examination of tables 2, 3, 4 and 6, where it will be found that 
in the six instances the average of the largest fibers appears 
greater in three instances on the right side and in three instances 
on the left side. i 
INCREASE AND DECREASE IN NUMBER OF FIBERS WITH 
ADVANCING AGE 
In table 8 are brought together certain data from tables 2, 3, 4 
and 6 giving the ages of the animals and the number of fibers in 
the right and left peroneal nerves. 
These entries are arranged according to the age of the animal 
from 147 to 454 days. . 
They are divided into six age groups, the first group including 
animals from 147 to 150 days of age, the second, animals from 
151 to 154 days of age, the third, animals from 156 to 162 days 
of age, the fourth, animals 251 days of age, the fifth, animals 
335 days of age, and the sixth, animals 454 days of age. The 
average number of fibers in both right and left peroneal nerves 
was determined for each age group. The table shows that be- 
tween 147 and 251 days of age there is a steady increase in the 
number of peroneal fibers from 2037 in the first age group to 
2251 in the fourth age group, roughly about two fibers per day; 
from 251 days to 454 days represented by two groups of three 
animals each, the number of fibers decreases to 1971 fibers, the 
number at 335 days being intermediate. Between 251 days 
and 335 days there are no records to show when the maximum 
number of fibers is reached. 
SUMMARY OF RESULTS 
A preliminary test, in which a gray rat was forced to run con- 
tinuously for four hours, showed the sectional area of the pero- 
neal fibers to be 20.4 per cent less than in the corresponding 
fibers of the control animal. The axis-sheath relation showed 
