INVOLUNTARY MUSCULAR FIBRE 23 
cd 
the fibre-cells, for the most part, homogeneous when extended, or faintly 
marked with longitudinal striae No doubt dots are present in abundance ; 
but these, so far as I have observed them in the pig’s intestine, are distinctly 
exterior to the fibres, though adherent to their surface ; and I suspect them 
to be little globules of a tenacious connecting fluid. That the fibre-cells do 
stick very tightly together may be seen by drying a minute portion of the tissue, 
after which they will be found shrunk, and slightly separated from one another, 
but connected more or less by minute threads. 
To sum up the general results to which we are led by the facts above men- 
tioned. It appears that in the arteries of the frog, and in the intestine of the 
pig, the involuntary muscular tissue is composed of slightly flattened elongated 
elements, with tapering extremities, each provided at its central and thickest 
part with a single cylindrical nucleus embedded in its substance. 
Professor Kolliker’s account of the tissue being thus completely confirmed 
in these two instances, and the description here given of its appearance in the 
arteries of the frog’s foot being an independent confirmation of the general 
doctrine, there seems no reason any longer to doubt its truth. 
It further appears, that in the pig’s intestine the muscular elements are, 
on the one hand, capable of an extraordinary degree of extension, and, on the 
other hand, are endowed with a marvellous faculty of contraction, by which 
they may be reduced from the condition of very long fibres to that of almost 
globular masses. In the extended state they have a soft, delicate, and usually 
homogeneous aspect, which becomes altered during contraction by the super- 
vention of highly refracting transverse ribs, which grow thicker and more 
approximated as the process advances. Meanwhile, the ‘ rod-shaped’ nucleus 
appears to be pinched up by the contracting fibre till it assumes a slightly oval 
form, with the longer diameter transversely placed. 
I will only further remark that these properties of the constituent elements 
of involuntary muscular fibre explain, in a very beautiful manner the extra- 
ordinary range of contractility which characterizes the hollow viscera. 
1 The longitudinal striae above referred to are probably due to a fine fibrous structure in the sub- 
stance of the fibre-cells. When in London, last Christmas, I had, through the kindness of Dr. Sharpey, 
the opportunity of examining a specimen of muscle from the stomach of a rabbit, which he had pre- 
pared after Reichert’s method. The nitric acid had not only detached the fibre-cells from one another, 
but also brought out very distinctly in each muscular element the appearance of minute parallel longi- 
tudinal fibres, which seemed to make up the entire mass of the fibre-cell except the nucleus. Ina plate 
accompanying the paper on the Iris, before referred to, I gave figures of some fibre-cells with distinct 
granules arranged in longitudinal and transverse rows. This appearance, which, however, so far as 
my experience goes, is exceptional, and is hardly sufficiently marked to deserve the appellation ‘ dotted ’, 
is probably caused by unequal contractions in the constituent material.—April 2, 1857. 
