SECOND CERVICAL NERVE OF THE RAT 141 
Our findings seem to show that age has more influence on the 
number of medullated nerve fibers than has weight. In this 
regard our records disagree with the conclusion of Boughton (’06) 
for the oculomotor nerve of the albino rat. Reference to individ- 
ual records in table 1 shows very definitely that there is no such 
relationship between body weight and the number of medullated 
nerve fibers that two rats of different ages but the same body 
weight will be more likely to have the same number of medullated 
nerve fibers in the ventral roots of the second spinal nerve than 
those of the same age but different body weights. 
The statement also seems justifiable that rats of like age and of 
one litter tend to have the same number of medullated nerve fibers. 
Curve E, fig. 2, has been plotted to show the relation of the aver- 
ages for groups of rats of given ages to the averages for the num- 
ber of their nerve fibers, but as this curve introduces the age factor 
in addition to that of weight, it will be discussed in the following 
section. 
A considerable increase in the number of medullated nerve 
fibers occurs during the early life of the albino rat. This was 
noted by Hatai (03) for the ventral roots of the sixth cervical, 
the fourth thoracic and the second lumbar spinal nerves, and by 
Boughton (’06) for the oculomotor cerebral nerve. In the second 
spinal nerve the increase seems to be checked at an earlier period 
than in the regions mentioned by Hatai. After the thirty-sixth 
day of our series, (table 2 and fig. 2) there is no uniform increase 
in the number of medullated nerve fibers, although the increments 
of age are considerable. 
Hatai (’03) using the criterion of body weight, argued that the 
increase in number among the ventral root fibers continued to a 
later period. His maximum of weight was 264.3 grams, which 
might correspond to that of one of our one hundred and thirty- 
two day rats. Hatai’s conclusions were based on the findings 
from one rat of each weight, age and sex not noted. 
Boughton (’06) while noting age, weight and sex in his series 
for the oculomotor nerve, did not select his material systematically 
with respect to these factors. He obtained the maximum num- 
ber of medullated nerve fibers in a male of one hundred and thir- 
