MOVEMENTS OF VOLUNTARY MUSCLE. 
477 
times longer than the diameter of the fasciculus, a circumstance which abundantly 
evidences the strength and tenacity of this extremely delicate membrane. But other 
fractures will be much more partial, scarcely extending through more than a quarter 
or a half of the fasciculus ; in the gap thus formed, the untorn sheath will be evident 
by its margin, which has the appearance of being suspended from point to point, and 
can be traced along the border of the fasciculus. If only two contiguous strise be 
separated by the traction, the same thing is observable. These appearances are re- 
presented in figs. 29. 30. In fig. 31. is a fasciculus partially withdrawn from its 
sheath. 
It has been already shown that the mutual adhesion of the fibrillse is liable to vary 
in amount, sometimes to be almost wanting, and generally to be capable of being 
diminished by maceration. This circumstance affords a condition to prove the exis- 
tence of the sarcolemma ; for as long as that is entire the fibrillee are kept together, 
though but very loosely united, and merely fall asunder at the broken extremity, 
where alone they have space to do so. Thus the brush or tassel is formed, which is 
described and delineated by more than one writer, and which by showing the strise of 
the same size as the beads of the fibrillse, and here and there passing gradually unto 
them, convinced Fontana*, and afterwards Schwann-^, of their true composition. Some- 
times, by accidental violence, a recent fasciculus may be reduced to a pulpy mass, in 
which fragments retaining their strise are strewn in confusion, while the sheath may 
remain uninjured, and preserve all these parts from falling asunder (figs. 37. 38.). 
But there is another method by which the existence and some of the properties of 
the sarcolemma may be demonstrated. This depends on the fact that its contents 
swell considerably when subjected to the action of several fluids, especially acids and 
alkalies. Phosphoric, tartaric and citric acids, and potash, are what I have em- 
ployed most commonly. The sheath dilates at first, but soon grows tense; the effect 
of which on the fibrillee is, that they emerge at its open extremity, where the fasciculus 
has been broken off, and there swell in diameter ; or if their union is but slight, 
expand in all directions into a roundish mass or button. Occasionally, in thus emerg- 
ing, they curl back upon itself the rim of the sarcolemma , which then is seen to grasp 
them still more tightly (see fig. 47. a. a.). But if this vent be insufficient, and espe- 
cially if the fragment be long, so that its ends cannot be reached soon enough, the 
over-distended membrane gives way, bursting at detached points, and allowing the 
escape of the contents. The hernise thus formed (figs. 39. 40.) admit of easy and 
close scrutiny by the microscope. They are very peculiar, and curiously illustrate 
the account I have given of the internal structure of the fasciculus. The fibrillse are 
not broken, but protrude sideways in loops more or less decided. Nor is the adhesion 
by which they are mutually held together dissolved ; although, as all are not alike 
distorted from their true position, it is so far disturbed, that the strise no longer 
possess their usual characteristics. The segments of the protruded fibrillse ceasing 
* Sur le Venin de la Vip&re, p. 229. f Muller’s Physiology by Baly, p. 8S0. 
