INVOLUNTARY MUSCULAR FIBRE. 553 



amined* each one presenting tapering extremities about equidistant from a single 

 elongated nucleus. The fibre-cells were of soft and delicate aspect, generally ho- 

 mogeneous 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 muscu- 

 lar 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 extremities, 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 deli- 

 cate homogeneous fibre-cells above described, every possible gradation could 

 be traced. Figs. 8 and 9, are somewhat longer than those just indicated, and 

 are also remarkable for their regularity. In figs. 5, 6, and 7, are repre- 

 sented fibre-cells of considerable length, marked here and there with highly 

 refracting transverse bands, in the intervals of which they are of soft and de- 

 licate aspect. In several cells one half was short, with closely approxima- 

 ted 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 being produced 

 by the whole material of the long muscular elements being drawn together into 

 so small a compass. The rounded appearance of the nuclei was accounted for 

 by supposing either that they had themselves contracted, or that they had been 

 pinched up by the contracting fibres, of which explanations the latter appears 

 the more probable. 



In order to place the matter if possible beyond doubt, I prepared two conti- 

 guous portions of the circular coat of a contracted piece of intestine in different 

 ways ; the one by simply cutting off a minute portion with sharp scissors, so as 

 to avoid as much as possible any stretching of the tissue, the other by purposely 

 drawing out a fasciculus to a very considerable length, and then teasing it with 

 needles. In the former preparation, the fibre-cells appeared all of them more or less 

 contracted, except in parts where the slight traction inseparable from any mode of 

 preparation had stretched the pliant tissue, which in the fresh state appears to 

 yield as readily to any extending force as does a relaxed muscle of a living limb. 

 In the other object, where the tissue had been purposely stretched, most of the 

 fibre-cells were extended, and possessed elongated nuclei. Here and there one 



VOL. XXI. PART IV. 7 K 



