156 journal of Comparative Neurology and Psychology. 



cation of about 600 diameters. Under these conditions the 

 "small" fibers could not be seen very distinctly. To distinguish 

 "large" from "small" fibers at any age, the following method 

 was employed: First, the total number of fibers as shown in the 

 photograph was counted, identifying each by reference to the 



BODT'TTEIGHT. 

 GRAMS. 

 390 



rio.n. 



jfo.or 



TIBHES. 



36 O 



330 



300 



270 



240 



;io 



18 O 



150 



120 



.90 



60 



30 



Til)res-Day« Curre 

 / 



GToirHi Curre 

 [drains daysl 



1 



1500 



1350 



1200 



1050 



000 



750 



600 



450 



300 



150 



DATS 30 



60 



90 



120 



150 



700 



rso 



Fig. 2. Showing the relation between the growth curve (grams-days) and the fibers-days curve 

 (oculomotor nerve) in the white rat. 



original section, viewed through a microscope, and then the plainly 

 visible, "large," fibers were counted without referring to the micro- 

 scope. The diff^erence between these two results was taken as the 

 number of "small" fibers. The rat of two years may be taken as 



