INVOLUNTARY MUSCULAR FIBRE 19 
directed chiefly to the hollow viscera, I thought it best to examine the tissue 
in some such organ. For this purpose I obtained a portion of the small intes- 
tine of a freshly killed pig, selecting that animal on account of the close general 
resemblance between its tissues and those of man. The piece of gut happened 
to be tightly contracted, and on slitting it up longitudinally, the mucous 
membrane, which was thrown into loose folds, was very readily detached from 
the subjacent parts. I raised one of the thick, but pale and soft fasciculi of the 
circular coat, and teased it out with needles in a drop of water, reducing it 
without difficulty to extremely delicate fibrils. On’ examining the object with 
the microscope, I found that it was composed of involuntary muscular fibre, 
almost entirely unmixed with other tissue, reminding me precisely of what 
I had seen in the human sphincter pupillae, except that the appearances were 
more distinct, especially as regards the nuclei, which were clearly apparent 
without the application of acetic acid. Several of the fibre-cells were isolated 
in the first specimen I examined, each one presenting tapering extremities 
about equidistant from a single elongated nucleus. The fibre-cells were of soft 
and delicate aspect, generally homogeneous or faintly granular, with sometimes 
a slight appearance of longitudinal striae, such as is represented in Fig. 4. 
I had now seen enough to satisfy my own mind that the involuntary 
muscular fibre of the pig’s intestine was similarly constituted with that of the 
human iris and the frog’s artery: but before throwing up the investigation, 
I thought it right to examine carefully some short, substantial-looking bodies 
of high refractive power, which at first sight appeared, both from their form 
and the aspect of their constituent material, totally different in nature from 
the rest of the tissue. Several of these bodies are represented in Figs. 10-15. 
Each is seen to be of somewhat oval shape, with more or less pointed ex- 
tremities, and presents several strongly marked, thick, transverse ridges upon 
its surface ; and each, without exception, possesses a roundish nucleus whose 
longer diameter lies across that of the containing mass.. Yet between these 
bodies and the long and delicate homogeneous fibre-cells above described, 
every possible gradation could be traced. Figs. 8 and g are somewhat longer 
than those just indicated, and are also remarkable for their regularity. In 
Figs. 5,6, and 7 are represented fibre-cells of considerable length, marked here 
and there with highly refracting transverse bands, in the intervals of which they 
are of soft and delicate aspect. In several cells one half was short, with closely 
approximated rugae, the other half long and homogeneous. Hence it was 
pretty clear that the appearances in question were due to contraction of the 
fibre-cells, and that the shortest of these bodies were examples of an extreme 
degree of that condition ; their substantial aspect and considerable breadth 
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