DIAMETERS OF NERVE CELLS AND FIBERS 533 
ered. In each instance, both for cells and for fibers, the values 
given in tables 2 to 6 are averages based on ten measurements. 
In table 2 are given the values for the diameters of the largest 
nerve fibers found in the seventh spinal nerve and in the dorsal 
and ventral spinal roots, respectively, in twelve albino rats rang- 
ing from 18.7 to 316.3 grams in body weight. The measurements 
are not only for the entire fiber, but for the axis also. At the 
bottom of each column is given the ratio of the diameter at 18.7 
TABLE 2 
Giving in micra the mean diameters of the largest entire fibers in the seventh cervical 
nerve and in the ventral and dorsal roots, together with the diameters of their respec- 
tive axes. The ratio between the first and the last measurement stands at the bottom 
of each column 
SEVENTH NERVE JUST 
VENTRAL ROOT DIAMETER] DORSAL ROOT DIAMETER | DISTAL TO THE GANGLION 
BODY WBIGET DIAMETER 
Entire fiber Axis Entire fiber Axis Entire fiber Axis 
grams 
18.7 8.8 5.5 8.6 5.4 8.9 5.6 
25.0 11.5 Wise 11.8 7.5 11.4 7.2 
43.3 11.9 We, 12.0 7.8 11.9 7.5 
59.2 12.1 (foe 12.3 7.9 12.2 Wot! 
81.0 12.8 7.6 13.2 7.8 13.0 8.0 
115.1 13.2 9.0 13.6 9.8 13.6 9.8 
120.3 14.3 9.8 14.5 10.0 14.3 9.6 
149.3 14.6 9.8 14.8 9.6 15.0 9.8 
178.0 17.6 12.7 17.8 12.2 18.1 12.6 
233.1 16.7 12.4 Weil 12.4 16.9 12.0 
243.1 17.6 11.6 17.6 13.4 WG 13.2 
316.3 20.2 14.0 20.3 14.3 19.8 14.2 
Ratios....... 12s W255 13253 1:2.6 1: 2.2 1:2.5 
grams to that at 316.3 grams of body weight. For the entire 
fiber this ranges between 2.2 for the fibers from the nerve and 2.3 
for both the ventral root and dorsal root fibers. The difference 
is so slight that we conclude that all three sets of fibers increase in 
diameter by the same amount. When the ratios for the axes 
are considered, it is seen that they also are nearly alike (i.e., from 
2.5 to 2.6), but higher than those for the entire fiber, showing 
that the axis is growing in diameter somewhat more rapidly than 
