554 MR LISTER ON THE MINUTE STRUCTURE OF 
would be seen of excessive tenuity, scarcely broader at its thickest part than the 
nucleus, looking, under the highest magnifying power, like a delicate thread of 
spun glass. To how great a length the fibre-cells admit of being drawn out in 
this way without breaking I cannot tell. Fig. 1 represents a portion of such a 
fibre with the contained nucleus. Among these extended fibres, however, there 
lay, here and there, an extremely contracted one, the result, I have no doubt, of 
the irritation 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 48 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 varying 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 contraction so frequent in muscle from the 
same piece of intestine 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 des- 
titute of transverse ruge, so that the point was now distinctly proved. 
Koxrixer, in his original article in the Zeitschrift fiir Wéissensehaftliche 
Zoologie, figured some long fibre-cells with transverse lines upon them,— 
“ knotty swellings,” as he termed them, which he supposed probably due to con- 
traction, 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 ap- 
pendages 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 ren- 
der the fibres indistinct, but the nuclei 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. 
