SECOND CERVICAL NERVE OF THE RAT ail 
heavier individual tends to have the larger average size of the 
largest nerve fibers. To this law there are a few exceptions, but 
in each instance the individual of greater weight but with the 
smaller nerve fibers was found to have a greater number of nerve 
fibers in this spinal root. 
The correlation, then, is not between body weight and size of 
the nerve fibers, but between body weight on the one hand and 
number and size of the nerve fibers on the other hand. Of the 
two factors, the size of the fiber is more affected by the body 
weight than by the number of fibers. The larger fibers may be 
found with greater body weight and greater number but when less 
size of fibers is found with greater body weight the compensating 
factor is the increased number of nerve fibers. This relation 
appears to be an argument in the establishment of a definite 
relation between the amounts of innervated and innervating mate- 
rial. 
Size of the fibers appears to have little relation to the body 
weight when the sexes are considered together. There are but 
slight deviations in size of the largest medullated nerve fibers in 
males and females of the same age but of widely diverse weights. 
Body weight without regard to age is misleading when used for 
a.criterion of the size of nerve fibers. Selecting at random from 
table 1 a male and a female of a weight less than 200 grams, one 
might chance upon a female of 187.96 grams weight and a male 
of 189.70 grams weight. ‘The male however is seventy-four days 
old, the female two hundred and seventy days of age. The male 
has seven hundred and twenty-six medullated nerve fibers in the 
ventral root of the second cervical nerve, the female eight hundred 
and fifty-three fibers. The average area of the ten largest medul- 
lated nerve fibers in the male is 117.67 square micra and of their 
axes 52.81 square micra, while for the female the average area 
for the fibers is 261.87 square micra and for their axes 131.92 
square micra. This may be analogous to the condition found in 
the spinal cord by Donaldson (’08, p. 371). In those findings, in 
rats of the same body weight without regard to age, female rats 
were found to have heavier spinal cords than the males. The 
