10 LISTER, ON INVOLUNTARY MUSCULAR FIBLE. 
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. Hach 
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 delicate homogeneous fibre-cells 
above described, every possible gradation could be traced. 
In several cells one half was short, with closely approxi- 
mated rugze, 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 ac- 
counted for by supposing either that they had themselves 
contracted, or that they had been pinched up by the con- 
tracting fibres, of which explanations the latter appears the 
more probable. 
In order to place the matter if possible beyond doubt, I 
prepared two contiguous portions of the circular coat of a 
contracted piece of imtestine 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 consi- 
derable 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 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 
