546 HENRY H. DONALDSON AND G. NAGASAKA 
the range of body weight which we have used is similar in both 
nerves. In the second and seventh cervical nerves, therefore, 
the ventral root fibers grow in diameter at the same rate. 
It will be noted that in table 2 the diameters of the ax’s cyl- 
inders are given for each group of nerve fibers. In 1905 Donald- 
son and Hoke published a series of observations on the areas of 
the axis cylinder and of the myelin sheath as seen in cross-sections 
of the spinal nerves of vertebrates. Since that time several sim- 
ilar determinations have been made, and it was thought impor- 
tant to have a determination made in this study also, since it 
permitted the comparison of the fibers in the ventral and dorsal 
TABLE 10 
Giving the areas of nerve fibers and their axes in square micra—also the percentage 
of the total area occupied by the axis, based on groups of three, from table 2 
IN THE SEVENTH CER- 
VENTRAL ROOT FIBERS | DORSAL ROOT FIBERS VICAL DISTAL TO THE 
SPINAL GANGLION 
AVERAGE a 
ari cob ates Areas g S Areas 8 6 Areas 3 a) 
Ent.F.| Axis | 584 /Ent.F| Axis | $94 |Ent.F| Axis | § ae 
grams days 
29.0 24 89.9) 36.3 40 91.6) 37.4 41 89.9} 36.3 40 
85.1 56 12686|ole5 41 13250) 5One 43 130.6} 56.7 43 
149.2 105 188.6} 91.6 48 193.5) 88.3 46 196.0) 89.9 46 
264.2 267 260 .0/126.6 49 262 .9}141.0 53 257 .2)134.7 52 
roots and in the nerve trunk near the ganglion, in respect of this 
character. In table 2 are given the diameters of the axes of the 
three classes of nerve fibers, and it has already been pointed out 
that the axes increase in diameter slightly more rapidly than do 
the entire fibers. 
Using the diameters just mentioned the areas of the entire 
fiber and of the axis (considered as circles) have been computed 
and entered in the condensed table 10. 
The columns which show the percentage of the entire area of 
the fiber represented by the axis reveal several interesting rela- 
tions. In the first place, the order of percentages is the same in 
the three classes of fibers and their absolute values at the same 
