ON” THE MINUTE STRUCTURE 
OF INVOLUNTARY MUSCULAR FIBRE 
[Transactions of the Royal Society of Edinburgh, vol. xxi, Part IV (1857), p. 549.] 
Read December 1, 1856. 
Ir has been long known that contractile tissue presents itself in the 
human body in two forms, one composed of fibres of considerable magnitude, 
and therefore readily visible under a low magnifying power, and marked very 
characteristically with transverse lines at short intervals, the other consisting 
of fibres much more minute, of exceedingly soft and delicate aspect, and 
destitute of transverse striae. 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 Kolliker of Wiirzburg announced that the tissue was 
resolvable into simple 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 juxta- 
position in the tissue, adhering to each other, as he supposed, by means of some 
viscid connecting substance. In the following year the same distinguished 
anatomist gave a fuller account of his discovery in the first volume of the 
Zeitschrift 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 previously known to occur, and also in situa- 
tions, 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 recognize 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 
