SECOND CERVICAL NERVE OF THE RAT 143 
in the central nervous system. More than this they are upon 
individuals other than those from which the ventral root fiber 
records were made. Comparable records may yet be secured for 
the material upon which the present report is made. The plane 
of the section which was necessary to make measurements on the 
ventral roots peripheral to the ganglia reliable made similar 
measurements upon the dorsal roots unreliable. If some control 
for the measurements can be devised, the counts will also be made. 
Whatever may be the significance of the presence of the added 
fibers the determination of the time and manner of their appear- 
ance must be of importance. 
The albino rat becomes sexually mature about the beginning of 
the third month of extra-uterine life, or‘about the seventieth day, 
but its increase in body weight may continue, to the end of the 
second year of life. According to the present records the average 
daily increase in weight between the ages of seven and fourteen 
days is 1.74 grams, and the average daily fiber increase is twenty- 
seven fibers. The average daily increase between fourteeen days 
and thirty-six days is 0.95 grams and 3.6 fibers. The incre- 
ments of age and weight are too great to establish these averages 
as final, but they undoubtedly show the general growth relations. 
The rate of increase in the number of medullated nerve fibers, 
in essential agreement with Hatai (03) and Boughton (06) 
diminishes with age. In our series the fourteen day period marks 
the greatest increase. : 
That such an increase in the number of medullated nerve fibers 
occurs in other animals has been shown by Boughton (’06) for 
the cat and suggested by Willems (11) for the rabbit. Boughton 
(06) used a mother cat and her five kittens, two males and three 
females. An increase in the number of medullated nerve fibers 
of the oculomotor nerve is shown among the kittens from one day 
to one hundred and eighty-two days, with the exception of the 
female at ten days, but the mother cat at thirteen years has a 
number of fibers not quite equal to that of the kitten of fifty-six 
days. 
Willems’ records (’11) were offered to show the relation of large 
and small nerve fibers in the portio minor of the fifth cerebral 
