INVOLUNTARY MUSCULAR FIBRE 21 
and he repeats this hypothesis in the part of his Mikroskopische Anatomie 
published in 1852. The proof of the correctness of this idea is now, I believe, 
given for the first time. 
The bearings of these observations on the main question respecting the 
structure of involuntary muscular fibre are obvious and important. In the 
first place, if the short, substantial bodies were mere contracted fragments 
of rounded fibres of uniform width, we should expect them to be as thick at 
their extremities as at the centre, instead of which they are always more or 
less tapering, and often present a very regular appearance of two cones applied 
to each other by their bases. Secondly, the uniform central position of the 
nuclei in the contracted fibres, proves clearly that the former are no accidental 
appendages of the latter, to which it seems difficult to refuse Kolliker’s appel- 
lation of cells. 
The effect of acetic acid on the involuntary muscular tissue is to render 
the fibres indistinct, but the nuclel more apparent; and if this reagent be 
applied to a piece of contracted muscle, many of the nuclei are seen to be of 
more or less rounded form. The deviation of the nuclei from the ‘ rod-shape ’ 
has hitherto been a puzzling appearance, but is now satisfactorily accounted for. 
In examining a fasciculus that had been fully stretched, forty-eight hours 
after death, I met with several good specimens of isolated fibre-cells, two of 
which are represented in Figs. 2 and 3. I would draw particular attention to 
the delicate, spirally twisted extremities of the fibre-cell 3, such as no tearing 
of a continuous fibre could possibly have produced. Though these fibres are 
very long, yet we have no reason to believe that anything near the extreme 
degree of extension has been attained in them, and we cannot but contemplate 
with amazement the extent of contractility possessed by this tissue. 
In Fig. 16 is represented a portion of a fibre-cell curled up, which has been 
introduced for the sake of the clear manner in which it shows the position of 
the nucleus embedded in it. Just as in the case of the fibres wrapped round 
the arteries of the frog’s foot, this cell might be seen in section by proper adjust- 
ment, and that section is observed to be oval; proving that the fibre is not 
round, but somewhat flattened. It happens that the nucleus appears at this 
point ; its section is circular, and is surrounded on all sides by the substance 
of the cell. 
The pig’s intestine seems to be a peculiarly favourable situation for the 
investigation of unstriped muscle. Judging from Kélliker’s measurements, 
the fibres appear to be of much larger size there than in the same situation 
in the human body. The length of the fibre-cell 3 is 1-37th of an inch. The 
fibre 2 is imperfect at one extremity ; but, taking the double of the distance 
