THE INFLUENCE OF AGE, SEX, WEIGHT AND RELA- 
TIONSHIP UPON THE NUMBER OF MEDULLATED 
NERVE FIBERS AND ON THE SIZE OF THE LARGEST 
FIBERS IN THE VENTRAL ROOT OF THE SECOND 
CERVICAL NERVE OF THE ALBINO RAT 
ELIZABETH HOPKINS DUNN 
From the Hull Laboratory of Anatomy, The University of Chicago 
Six FIGURES 
So much has been published regarding the growth of the medul- 
* lated nerve fiber that an explanatory word may be permissible 
on offering a paper which duplicates in many particulars the 
findings of other investigators. 
The collection of the data presented here was suggested in 
1903 by an examination of the control, or normal, material used 
by Dr. S. W. Ranson for his study of the spinal ganglion. Of the 
sectioned material, that for five rats of the thirty-one here re- 
ported was generously furnished by Dr. Ranson. In examining 
that material the salient feature was, to me, the increase in size 
of the medullated nerve fibers in the older rats, and it seemed 
desirable to ascertain if possible what conditions other than age 
might influence the size of these fibers. This point seems to 
have attracted other interest, since in 1906 Dr. Boughton 
published important data regarding the increase in size with age 
and weight of the medullated nerve fibers of the oculo-motor 
nerve in the albino rat and in the cat from a mixed series of males 
and females. 
While the chief point of my inquiry was so admirably elucidated 
by Dr. Boughton’s paper, there seemed to be place for the more 
extended study with defined categories which I had undertaken. 
Inquiry was made before continuing the work as to the existence 
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THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 2 
