MYELINATED FIBERS—-PERONEAL NERVE OF RAT 415 
cases the two sides are within 1 per cent of one another; in 8 of 
the remaining eleven cases the average of the 40 largest fibers is 
greater on the right side. 
The axis sheath relation here is practically 40 per cent axis to 
60 per cent sheath. 
Taking the 15 cases together, the average size of fibers of the 
right peroneal is 96.8 square micra, the average of the left 91.5 
Square micra, the difference being 5.2 square micra, indicating 
that the largest fibers of the right peroneal nerve are more than 
5 per cent greater than those of the left. 
Examining these results by statistical methods we obtain the 
following table 7. 
TABLE 7 
Right peroneal fibers Left peroneal fibers 
M (mean) 96.8 sq. micra Mz = + 1.3 M (mean) 91.5 sq. micra M, = = 1.6 
o 7.6 Go = +09 o 9.7 G6 = = 11 
C 7.9 Ce= += 0.9 C 10.6 Ce = += 1.8 
The observed difference between the average sectional area 
of right peroneal fibers and left peroneal fibers as shown by 
table 7 is 5.2 square micra. 
The probable error of this determination is +2.1; a little more 
than one-third of the difference observed. 
If, however, the first seven entries of table 6 be considered 
separately the average of the right peroneal fibers is found to be 
7.7 square micra greater than the average of the left peroneal 
fibers, while in the last eight entries this difference is only 3.1 
square micra. If No. 342, which presents the greatest difference 
between the right and left fibers, be omitted, then the average 
of the right peroneal fibers becomes 96.4 instead of 96.8 and 
the average of the left peroneal fibers becomes 92.7 instead of 
of 91.6, and the difference becomes 3.7 instead of 5.2 square 
micra. 
From the statistical examination of table 6 and this further 
analysis of its contained data we may safely assume that the 
difference here shown between the sectional areas of the largest 
fibers of the left peroneal nerve and those of the right peroneal 
