136 EDWARD SCHAFER. 
acuminate processes. Its substance either appears granular, or 
more homogeneous, and refracting the light strongly ; in the 
first case the fibrils composing the central fibre may often be 
seen to spread out into the substance of the enlargement ; in the 
second this last is probably covered with a thin layer of white 
substance similar to that composing the medullary sheath of 
the nerves, and the arrangement of the fibrils 1s thus obscured. 
The terminal enlargement as well as the remainder of the 
central fibre becomes deeply stained by chloride of gold, much 
more deeply than the substance composing the surrounding 
core, but even in very successfully stained preparations I 
have hitherto failed to discover a fine network of nervous 
fibrils around the extremity, as described by A. Budge. If 
the terminal enlargement is of considerable size it may con- 
tain a clear, round nucleus, with nucleolus, generally ob- 
scured by the granular substance of the enlargement. A 
nucleus is not, however of frequent occurrence, as Jacubo- 
witsch and Ciaccio have described. 
It is not at all uncommon to find the central fibre accom- 
panied for a short distance within the core by the white sub- 
stance of the medullary sheath (B, fig. 3); this has been 
noticed by various observers, as well as the fact that the 
white substance may reappear here and there, especially at a 
bend in the core; I have besides in more than one instance 
noticed the medullated fibre passing quite through one Paci- 
nian (generally a smaller one) to terminate in another, with- 
out loss, or even diminution in thickness, of its medullary 
sheath (A, fig. 3). Axel Key and Retzius also describe the 
fibre as occasionally retaining the medullary sheath as far as 
the terminal enlargement. Ordinarily there is no medullary 
or white substance surrounding the fibre in its course; this 
fact is readily determined by the action of osmic acid, which 
speedily blackens the fatty substances which mainly compose 
the medullary sheath of the nerves. 
Sometimes, when the central fibre bifurcates, one of the 
branches may retain a medullary sheath and the other be 
continued as a pale fibre. 
With regard to the presence or absence of a membranous 
structure corresponding to the primitive sheath (Schwann’s 
sheath) of the nerves, it will be sufficient here to state that 
no indication of such a structure could be detected immediately 
investing the central fibre, either when viewed longitudinally 
or in transverse section, nor any nuclei in the immediate 
neighbourhood of the fibre which might belong to such a 
sheath. 
In its behaviour to staining fluids the central fibre of the 
