56 JOURNAL OF COMPARATIVE NEUROLOGY. 
sections were made on paper and the areas determined by two 
methods: 
(a) The projections were lithographed and printed on 
paper of a uniform thickness, the weight of a square mm. of 
which had been determined beforehand by several weighings. 
The outlines of the fascicles in the projections were then cut 
out and weighed. To obtain in sq. mm. the area of the pro- 
jection of the cross-section of a given root, the weight of the 
paper so cut out was divided by the weight of one sq. mm. 
To reduce the area of projections to the true area of the cross- 
sections of the roots they were divided by the square of the 
Jinear magnification of the projections. 
(b) The outlines of the fascicles as projected on paper 
were measured by means of a planimeter and their areas found 
in sq. mm. from its readings. The areas of the projections 
were then reduced to true areas. As the results obtained by 
the two methods are practically the same, only those deter- 
mined by the planimeter are given in Table I*. His results 
for the ventral roots are also omitted as not necessary for our 
comparison. 
3. Authors Determination. ‘The material used in this in- 
vestigation was from a middle-aged man, weighing 180 lbs., 
and killed by accident. The spinal cord, together with the 
roots, was removed within eight hours after death, and hardened 
in MULver’s fluid for one month, the fluid being changed every 
day during the first part of the period of hardening. The dor- 
sal roots of the left spinal nerves were embedded in celloidin 
and sectioned at the place, between the cord and the spinal 
ganglia, where they penetrate the dura mater. 
Although we speak, of these roots as all from the left side 
of this subject, in one instance this was not the case. The 
dorsal root of Th. IX was from the right side, the one on the 
left having been injured in removal. The left dorsal root of C, 
I was wanting in this subject, andthe one used was from a dif- 
ferent man weighing about 140 lbs. This was obtained for me 
by the courtesy of Dr. PeTeR Bassor. There is, however, 
