512 
grow dark, The addition of a little acid, how- 
ever, swells the fibre, obliterates the cross lines, 
and brings the corpuscles into view, not only 
at this early ati but at every subsequent 
one, even to old age. In insects, the nuclei 
in the earliest stage are a single or double 
series in the axis of the fibre, and in the per- 
fect fibre they hold the same position (figs. 
292 and 293, c). In the Vertebrate classes 
they have a like correspondence, being scat- 
tered equally throughout the mass, in both 
foetal and adult states. Where the fibre is 
small, however, they usually abound more 
towards the surface. They are oval and flat, 
and of so little substance, that though many 
times larger than the primitive particles, and 
lying amongst them, they do not interfere 
with their mutual apposition and _ union. 
These corpuscles are frequently the cause of 
irregular dark longitudinal streaks, seen in the 
fibre by transmitted light. They usually contain 
some central granules or nucleoli (fig. 295). 
It is doubtful whether the corpuscles or nuclei 
originally present remain through life, or whe- 
ther successive crops advance and decay during 
the progress of growth and nutrition. But it 
is certain, that, as development proceeds, fresh 
corpuscles are deposited, since their absolute 
number is far greater in the adult than in the 
fetus, while their number, relatively to the 
bulk of the fibre, at these two epochs, remains 
nearly the same. 
7. Of the sarcolemma, or tunic of the ele- 
mentary fibre.—This is a simple transparent 
homogeneous membrane of extreme tenuity, 
but very tough and elastic, which, in the form 
of a perfect tube, invests every elementary fibre, 
adheres to its surface, and isolates it from sur- 
rounding parts. It is universally present in vo- 
luntary muscles, and may be demonstrated in a 
variety of ways. When the fibres have been im- 
mersed in alcohol, which causes them to shrink, 
it is often seen wrinkled on their surface; or 
when they are cracked or broken across, it fre- 
quently remains entire and connects the severed 
fragments (fig. 294). This method of showing 
Fig. 294. 
Fragments of an elementary fibre of the Skate, held together 
by the untorn but twisted sarcolemma. 
a, Sarcolemma. 
it is best followed in the case of the large and 
brittle fibres of the Skate; or, it may be seen 
cutacross in a general transverse section of a 
dried muscle (fig. 290). When the texture 
of the fibre is destroyed by maceration, the 
broken mass is sometimes retained hy the 
sheath, which thus becomes visible. hen 
the fibre swells by acid, this tunic resists, and 
MUSCLE. 
b, b, opposite fragments of the fibre. 
the swollen mass emerges at its broken a 
open end : but, if this is not effected with 
ficient celerity, the sarcolemma may give 
at different points, being burst by the n 
which thus forms hernie. Such 
masses being unequally stretched have the 
transverse and longitudinal lines distorted fro: 
their true direction and thrown into v 
gant curves (fig.295), Again, if a fibre st 
Part of an elementary fibre from the human 
ject, treated with ic acid, 
a, point at which the sarcolemma is burst. 
b, hernia of the sarcous mass, with di 
of the longitudinal and transverse lines. 
c, a smaller hernia. 
les are seen scattered throughout the 
and some detached ones, d, are represented below. T 
average diameter is one-thousandth of an English 
_ 
retaining its irritability, be immersed in wate 
this fluid, on being absorbed, excites cor 
tion, by which it is immediately expelled 
among the primitive particles. hen tl 
forced out it usually collects between 
fibre and its sheath, raising the latter 
form of bulle (figs. 301 and 302, an¢ 
Muscutar Morton). The progress of t 
teresting phenomenon evinces the adhesio 
exists between the fibre and its sheath. 
bulla immediately subside, by 
transudation of their fluid, when 
part is placed in thick syrup. 
met with a singular demonstratit 
the existence and properties 0 
colemma, in finding it filled 
merous trichine (fig. 296), whi 
taken the place of the contractil 
terial, the sheath preserving all its 
racteristic beauty and transparen 
I discovered this remarkab 
brane in Insects, Crustacea, a 
the tribes of Vertebrata, in 18; 
knowing that Professor Schwann had 
viously described it in connection with the 
velopment of muscle in Insects and * 
He believes it to be a persistent po 
the membrane of the original ce 
oh 
* Auct. loc. cit. p. 480, 
1. xvii 41-5 
t Mikros. Untersuch. p. Yes, Ph 
