15 4 ELIZABETH HOPKINS DUNN 
amount of medullation and size of the fibers might increase the 
weight of the cord. 
A further step in the comparison of males and females of the 
same ages but of different weights is the recognition of the fact 
that among mature rats, the females, which rarely attain the 
weight of the males, must have a mass or bulk of the peripheral 
nervous system much greater in proportion to the body weight 
550 
300 
200 
100 
Fig.5 F is plotted to show the body growth for the female rats of each group 
and G the curve for the male rats of the same groups. These curves are to be con- 
trasted with those in fig. 6, which show the curves for the growth of the largest 
nerve fibers. 
than that of the males. Increased weight in the spinal cord in 
the female has been interpreted as due to the richness of visceral 
innervation, especially of the pelvic organs. But in this second 
cervical nerve an excess over the males is found with very few or no 
