LISTER, ON INVOLUNTARY MUSCULAR FIBRE, 9 
be cylindrical. These fibre-cells are from z}5 inch to 735 
inch in length, from 3355 inch to 3,555 inch in breadth, and 
about z3!55 inch in thickness, measurements on the whole 
rather greater than those given by Kolliker for the human 
intestine, the chief difference being that in the frog’s arteries 
they are somewhat broader and thicker. 
Now, the middle coat of the small arteries is universally 
admitted to be composed chiefly of involuntary muscular 
fibre; but in the vessels just described it consists of nothing 
whatever else than elongated, tapering bodies, corresponding 
in dimensions with Kolliker’s fibre-cells, and each provided 
with a single cylindrical nucleus imbedded in its substance. 
Considering, then, that no tearmg of the tissue had been 
practised in the preparation of the objects, but that the parts 
were seen undisturbed in their natural relations, it appeared 
to me that the simple observation above related settled the 
point at issue conclusively. 
It was, however, suggested to me by an eminent physiolo- 
gist, that the various forms in which contractile tissue occurs 
in the animal kingdom forbid our drawing any positive 
inference regarding the structure of human involuntary 
muscle from an observation made on the arteries of the frog. 
Beimg anxious to avoid all cavil, and understanding that Mr. 
Ellis’s researches had been 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 
intestine of a freshly killed pig, selecting that animal. on 
account of the close general resemblance between its: tis- 
sues and those of man. The piece of gut happened'to be 
tightly contracted, and on slitting it up longituglimally, the 
mucous membrane, which was thrown into loége folds, was 
very readily detached from the subjacent parts” E 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 mvoluntary muscular fibre, almost entirely unmixed with 
other tissue, reminding me precisely of what I had seen in 
the human sphincter pupille, 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 lon- 
gitudinal strie. 
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