ANALYSIS OF THE SYMPATHETIC TRUNK 453 
eleventh thoracic ganglia, stained with osmic acid, was cut into 
serial sections. In these it was possible to identify the ninth 
white ramus which contained a considerable number of normal 
myelinated fibers, of which the greater number were large. The 
fibers from this ramus could be followed as a superficial bundle 
down the trunk to the point where the tenth ramus entered. 
This contained in addition to the degenerated preganglionic fibers 
a considerable number of normal myelinated fibers, and of these 
there were rather more small than large ones. As each ramus 
entered it lay close to the crescentic field of unmyelinated fibers 
and the area of the tenth was immediately adjacent to that of the 
ninth. A little farther caudad it was no longer possible to sep- 
arate the two areas, the two together being spread out over nearly 
half the circumference of the trunk as shown in figure 9. In this 
figure the degenerated bundles are indicated by the stippled 
background. The myelinated fibers in these bundles are affer- 
ent, and it will be seen that they are of all sizes and there are about 
as many of one size as of another. 
Pyridine silver preparations of the twelfth thoracic internodal 
segment were especially instructive (fig. 10). The greater part 
of the trunk was normal and was characterized by the presence 
of great numbers of small myelinated fibers. Large myelinated 
and unmyelinated fibers were also in evidence. On one side 
there was seen a condensation of the unmyelinated fibers which 
represents the crescentic field normally present at all levels of 
the thoracic sympathetic trunk. Another area, rather sharply 
limited, from which the majority of the fine myelinated fibers 
had disappeared, contained myelinated fibers of all sizes in about 
equal proportion and also unmyelinated axons. The _ back- 
ground presented a peculiar reddish-yellow tone which we have 
found characteristic of degenerated fascicles stained by this 
method. It is obvious that the fine myelinated fibers had de- 
generated and that this is the same fascicle that is seen in figure 
9. A comparison of the two figures will show that the areas 
occupied by the degenerated fibers have undergone great shrink- 
age in passing through the steps of the pyridine silver technique, 
and because of this the large myelinated and unmyelinated fibers 
