556 MR LISTER ON THE MINUTE STRUCTURE OF 
Hence it appears that the length of the most contracted fibre-cell is the same as 
that of the nucleus of an extended one. The fibres vary somewhat in breadth, 
independently of the results of contraction. Thus, one in the extended condition 
which I sketched, but which is not here shown, measured only =, inch across. 
The nuclei of the uncontracted fibres are very constantly of the same length, and 
are good examples of the rod-shape to which KoLniKer has directed particular 
attention. They always possess one or two nucleoli, and have often a slightly 
granular character; occasionally, as in fig. 21, they present an appearance of 
transverse markings. One frequently sees near the nucleus of a fibre that has 
been artificially extended from the contracted state, an appearance of a gap in 
the substance of the cell, forming a sort of extension of the nucleus, as if the fibre 
generally had been stretched more completely than the nucleus: an example of 
this is presented by fig. 7. Mr Exuis lays great stress on a dotted appearance 
which he considers characteristic of involuntary muscular fibre. I must say I 
agree with KotxrKer in finding the fibre-cells, for the most part, homogeneous 
when extended, or faintly marked with longitudinal striz.* 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 sepa- 
rated 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 KoLLiKeER’s account of the tissue being thus completely confirmed in 
these two instances, and the description here given of its appearance in the arte- 
ries of the frog’s foot being an independent confirmation of the general doctrine, 
there seems no reason any longer to doubt its truth. 
* The longitudinal strie above referred to, are probably due to a fine fibrous structure in 
the substance of the fibre-cells, When in London, last Christmas, I had, through the kindness 
of Dr Suarpry, the opportunity of examining a specimen of muscle from the stomach of a rabbit, 
which he had prepared after Retcuert’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 longitudinal fibres, which seemed to make up the entire mass of 
the fibre-cell except the nucleus. In a plate accompanying the paper on the Iris, before re- 
ferred 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 une- 
qual contractions in the constituent material—2d April 1857. 
