LISTER, ON INVOLUNTARY MUSCULAR FIBRE. i} 
without breaking I cannot tell. Among these extended 
fibres, however, there lay, here and there, an extremely 
contracted one, the result, I have no doubt, of the irrita- 
tion produced by the needles upon the yet living tissue. In 
order to guard against this source of fallacy, I kept a piece 
of contracted gut forty-eight hours, and then examined two 
contiguous parts of the circular coat in the way above 
described. The muscle was much less readily extended than 
in the fresh state, and I found that, where stretching of the 
tissue had been avoided as much as possible, it was composed 
entirely of fibre-cells marked with transverse ridges of vary- 
ing thickness and proximity; a minute fibril having, under 
a rather low power, the general aspect represented in fig. 17. 
But I saw no distinct examples of the extreme degree of con- 
traction so frequent in muscle from the same piece of intes- 
tine in the fresh state. This confirmed my suspicion that 
the latter had been induced by the irritation of the mode of 
preparation. On the other hand, a fully stretched fasciculus 
showed its fibres everywhere destitute of transverse rugze, so 
that the point was now distinctly proved. Kdlliker, in his 
original article in the ‘ Zeitschrift ftir Wissenschaftliche Zoo- 
logie,’ figured some long fibre-cells with transverse lnes 
upon them—“ knotty swellings,” as he termed them,—which 
he supposed probably due to contraction, 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, sub- 
stantial 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 appellation of cells. 
The effect of acetic acid on the involuntary muscular 
tissue is to render the fibres indistinct, but the nuclei more 
apparent; and if this reagent be applied to a piece of con- 
tracted 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, 
