64 JOURNAL OF COMPARATIVE NEUROLOGY. 
nerves of man, I made use of the same material as was em- 
ployed in determining the areas of the cross-sections of these 
roots. The fascicles in the projections used for determining the 
areas, as is shown in Figs. 2-32, were numbered. Photo- 
graphs of some 200 diameters enlargement were made from 
small negatives of the cross-sections of the roots, and in these 
the fascicles were numbered as in the projections; in addition 
the sub-divisions of the fascicles were lettered. These sub- 
divisions were not made into individual fascicles, because the 
septa between them were not sufficiently well developed to war- 
rant it. Both the projections and the photographs were placed 
on the table in front of the microscope and used in cen 
the fascicles the fibers of which I wished to count. 
The sections were well stained and the fibers easily recog- 
nized in all buta few instances. The characteristic mark sought 
for in case of doubt is the ring-like appearance of a nerve fiber 
due to the transparency of its axis-cylinder. In rare cases, 
however, where a nerve fiber was sectioned through its node of 
RANVIER this characteristic was not prominent. By means of 
this characteristic a small nerve fiber is easily distinguished 
from a connective-tissue corpuscle or a fragment of the medul- 
lary sheath. Some difficulty was found in the _ obliquely 
sectioned fascicles because the axis-cylinder in such cases was 
not easily recognized. The amount of connective tissue in 
some of the thoracic roots was also a source of difficulty in that 
it made the sections denser by filling up the spaces between the 
nerve fibers, and thus tended to obscure the small fibers. It is 
not thought, however, that any important errors have been 
made as the result of the difficulties named. 
In counting, a ZEISS microscope fitted with a mechanical 
stage, a ZEISS objective, 4 mm., aperture 0.95, and oculus No. 
6 or 8, was used. Oculus No. 6 was used only in a few in- 
stances where a coarse-fibered fascicle or one of its sub-divisions 
was too large for the field of vision ina No. 8 oculus, but not 
too large for that in an oculus No. 6. 
In the oculus was placed an ocular micrometer ruled into 
square millimeters. The cross-sectioned nerve fibers seen with- 
