6 LISTER, ON INVOLUNTARY MUSCULAY FIBRE, 
principle of which is the heart, whose fibres are a variety of 
the striped kind. 
Till within a recent period the fibres of unstriped or invo- 
luntary muscle were believed to be somewhat flattened bands 
of uniform width and indefinite length, marked here and 
there with roundish or elongated nuclei; but in the year 
1847, Professor Kélliker of Wurzburg announced that the 
tissue was resolvable into simpler elements, which he regarded 
as elongated cells, each of somewhat flattened form, with 
more or less tapering extremities, and presenting at its 
central part one of the nuclei above mentioned. These 
* contractile” or “ muscular fibre-cells,” as he termed them, 
were placed in parallel juxtaposition in the tissue, adhering 
to each other, as he supposed, by means of some viscid con- 
necting substance. In the following year the same distin- 
guished anatomist gave a fuller account of his discovery in 
the first volume of the ‘ Zeitschrift fiir Waissenschaftliche 
Zoologie,’ and described in a most elaborate manner the ap- 
pearances which the tissue presented in all parts of the body 
where unstriped muscle had been previously known to occur, 
and also in situations, such as the iris and the skin, where 
its existence had before been only matter of conjecture, but 
where the characteristic form of the fibre-cells, and of their 
“rod-shaped ” nuclei, had enabled him to recognise it with 
precision. Confirmations of this view of the structure of 
involuntary muscular fibre were afterwards received from 
various quarters, one of the most important being the obser- 
vation made in 1849 by Reichert, a German histologist, that 
dilute nitric or muriatic acid loosens the cohesion of the fibre- 
cells, and enables them to be isolated with much greater facility. 
In 1852 I wrote a paper “On the Contractile Tissue of the 
Tris,” published in the ‘ Microscopical Journal,’ in which I 
gave an account of the involuntary muscular fibre contained 
in that organ in man and some of the lower animals, stating 
that the appearances I had met with corresponded exactly 
with Kdélliker’s descriptions, and illustratmg my remarks 
with careful sketches of several fibre-cells from the human 
iris, isolated by tearing a portion of the sphincter pupille 
with needles in a drop of water. In 1853, another paper by 
myself appeared in the same Journal, “ On the Contractile 
Tissue of the Skin,” confirming Kdlliker’s recent discovery 
of the “arrectores pili,’ and describing the distribution of 
those little bundles of unstriped muscle in the scalp. These 
and other investigations into the involuntary muscular tissue 
convinced me of the correctness of Kolliker’s observations, 
and led me to regard his discovery as one of the most beau- 
