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XXXIII.—On the Minute Structure of Involuntary Muscular Fibre. By Joseru 
Lister, Esq., F.R.C.S. Eng. and Edin., Assistant-Surgeon to the Royal 
Infirmary, Edinburgh. Communicated by Dr Curisrison. 
(Read 1st December 1856.) 
It has been long known that contractile tissue presents itself in the human 
body in two forms, one composed of fibres of considerable magnitude, and there- 
fore readily visible under a low magnifying power, and marked very character- 
istically with transverse lines at short intervals, the other consisting of fibres 
much more minute, of exceedingly soft and delicate aspect, and destitute of trans- 
verse strive. The former variety constitutes the muscles of the limbs, and of all 
parts whose movements are under the dominion of the will; while the latter 
forms -the contractile element of organs, such as the intestines, which are placed 
beyond the control of volition. There are, however, some exceptions to this 
general rule, the principal of which is the heart, whose fibres are a variety of the 
striped kind. 
Till within a recent period the fibres of unstriped or involuntary 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 KoLuiker of Wiirzburg announced that the tissue was resolvable into 
simpler elements, which he regarded as elongated cells, each of somewhat flat- 
tened 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 connecting sub- 
stance. In the following year the same distinguished anatomist gave a fuller 
account of his discovery in the Ist volume of the Zedischrift fiir” Wissenschaftliche 
Zoologie, and described in a most elaborate manner the appearances which the 
tissue presented in all parts of the body where unstriped muscle had been pre- 
viously 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 cha- 
racteristic 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 observation 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 Iris,” published in the Micro- 
VOL. XXI. PART IV. 71 
