NUMBER OF PRE- AND POSTGANGLIONIC NEURONES 361 
specimen the peripheral bundle of unmyelinated fibers formed a 
separate fascicle entirely outside of the perineurium of the trunk. 
The few myelinated fibers which this fascicle contained were 
descending from the ganglion and were not enumerated. .In the 
absence of large myelinated fibers which might possibly be inter- 
preted as being sensory, we believe that all of the fibers in the 
cephalic end ‘of the trunk proper are ascending preganglionic 
fibers (p. 317). So far as we can determine these fibers are not 
mixed with any unmyelinated axons. 
From these considerations it is evident that an enumeration 
of the myelinated fibers in the sympathetic trunk just below the 
superior cervical ganglion should give the number of preganglionic 
fibers entering the ganglion. We have also ascertained the 
number of cells in that ganglion and the ratio between these 
cells and the preganglionic fibers. 
TECHNIQUE 
The cervical portion of the sympathetic trunk was exposed for 
its entire length and fixed in osmic acid. During fixation it was 
held taut by stretching it over a glass cover-slip with fine silk 
threads tied at either end, the upper enclosing the branches of 
the internal carotid nerve well above the superior cervical gan- 
glion. All the other branches of the ganglion were cut off close 
to their origin. The tissue was blocked in paraffine and serial 
sections prepared, 10u in thickness, from the superior to the in- 
ferior pole of the ganglion, and sections 7 in thickness were made 
through the trunk. 
The number of fibers in the trunk was determined as follows. 
A ruled ocular, No. 10, was used, the ruling enclosing an area of 
1 sq. em. subdivided into one hundred forty-four smaller squares. 
The lines of the ocular were made parallel to the anteroposterior 
and lateral lines of movement of a mechanical stage, the latter 
being at right angles to each other. A 7a objective was used. 
Beginning at the left side of a section, the fibers within the area 
of the ruled square were counted. ‘Then, using only the antero- 
posterior movement of the stage, the section was moved the full 
