DIAMETERS OF NERVE CELLS AND FIBERS 547 
body weight are also very close in all three classes. Between 
105 days and 267 days the area of the axis approximates 50 per 
cent of the entire area; i.e., the area of the axis is equal to the 
area of the ring of myelin surrounding it. This ‘one to one’ rela- 
tion was that found by Donaldson and Hoke in 1905 (table VI, 
p. 9). That paper shows that in general the small fibers from 
young albino rats had an axis somewhat less than half the area 
of the fiber, while in the fibers from older rats this area was a 
trifle more than half that of the entire fiber, but in the study of 
1905 no attention was paid to age or to the abso'ute size of the 
fibers. In 1912 Dunn examined these relations in the second 
cervical nerve of albino rats from the standpoint of age, sex, 
TABLE 11 
Showing the percentage of the area of the entire fiber represented by the area of the 
axis in the ten largest fibers found in the ventral root of the second cervical nerve 
of the albino rat—Dunn (’12)—and in the ten largest fibers in the ventral root of 
the seventh cervical nerve of the albino rat, as shown in table 10 
DATA FROM TABLE 10 DATA FROM DUNN (’12) 
Age Area of axis Area of axis Age 
days per cent per cent days 
24 40 40 36 
56 41 44 75 
105 48 44 sy 
267 49 50 270 
and body weight. The relations are expressed by her (loc. cit., 
table 2, p. 135) as ratios of the area of the axis taken as one, to 
the area of the entire fiber. When, however, her data are recast 
in the form which we have chosen, and age is made the basis of 
comparison, there appear the relations shown in table 11. 
When the comparison is made, as in table 11, it appears that 
the axis-sheath relation is similar n the fibers forming the 
ventral roots of the second and the seventh cervical nerves, 
respectively, and that in both cases the ‘one to one’ relationship 
is attained in the oldest group. These nerves were all measured 
with the eyepiece micrometer. 
There are still other observations on this point. Greenman 
(13, table 9) reported at the proximal end of a bit of normal 
