STRUCTURE OF THE PACINIAN CORPUSCLES. 137 
Pacinian corpuscle precisely resembles the axis-cylinder of 
a nerve. 
The Core. 
The substance composing the core is commonly described 
as being alike throughout ; but in many corpuscles, if not in 
all, an outer nucleated part, of variable extent, may be dis- 
guished from the almost homogeneous, non-nucleated sub- 
stance which immediately surrounds the central fibre. On 
careful focussing, and under a high power of the microscope, 
the inner part presents an appearance of indistinct longitu- 
dinal striation, which in a transverse section appears irregu- 
larly concentric (see Plate VIII, fig. 2 A) ; the outer appears 
composed of protoplasmic cells, like connective-tissue cor- 
puscles, each with a clear oval nucleus; next to the inner 
part are a few flattened nuclei seen in section as mere lines. 
Osmic acid (as shown by Michelson), chloride of gold, 
hematoxylin, and most of the ordinary staining fluids, colour 
the whole core much as they colour protoplasm. 
The Capsular Envelope. 
The structure of this can only be properly elucidated by 
the study of sections and by teased preparations. Examined 
in the ordinary way, fresh, in an indifferent fluid, the core of 
the Pacinian corpuscle appears, as is well known, surrounded 
by and enclosed in a number of concentric membranous 
“capsules,” which, since Hoyer showed that treatment with 
nitrate of silver brings to view epithelioid markings upon 
them, have since been commonly regarded as composed each 
of a single layer of flattened cells with a certain amount of 
connective-tissue fibres, both white and elastic, on one or 
both surfaces. ‘The so-called capsules, also, appear separated 
from one another by a clear fluid, less in amount both close 
to the core and near the exterior of the corpuscle, so that at 
these parts the capsules appear closer together than in the 
intermediate region. 
But a new! view of the structure has recently been 
brought forward by Axel Key and Retzius, according to 
whom the supposed simple capsules each consist of two layers 
of flattened cells, placed, as it were, back to back ; and they 
draw attention to the fact, which had been previously pointed 
out by Ciaccio, that the intercapsular spaces are not merely 
filled with an albuminous fluid, but are, to a greater or less 
extent in different parts, pervaded by fibres both white and 
1 A somewhat similar view seems to have occurred to Henle and Kolliker, 
and to have been rejected by them. 
