Abstract
A HIGHLY interesting paper on the above subject was read before the Royal Society on April 3, by Mr. E. A. Schäfer, of University College. The muscle of the limbs of the large water-beetle formed the subject of the investigation, and it was examined immediately after removal from the living animal, without the addition of any reagent, to prevent the introduction of complications. According to the author, a muscular fibre consists of a homogeneous ground substance, which aopears at first sight to be formed of two distinct substances, one dim and the other bright, arranged in alternate discs at right angles to the direction of the fibre; and a vast number of minute rod-like bodies, imbedded in the protoplasmic basis, having their axes coincident with that of the fibre itself. These are termed muscle rods; in the muscle at absolute rest they are uniformly cylindrical, and produce the appearance of a simple longitudinal fibrillation in the fibre, with no transverse striping. But when in action these muscle-rods are terminated at each extremity by a knob, and are consequently dumb-bell shaped. It is these knobs which give the appearance of the line of dots which is always described as existing in the middle of each bright transverse band of the muscle fibre, whereas the dim one is that in which the shafts of the muscle-rods are imbedded. In contraction of the muscle, the heads of the rods become enlarged at the expense of the shafts, the extremities of each muscle-rod consequently approaching one another; and the enlarged heads come nearer to their neighbours of the same series, and to those of the next series which meet them in the bright stripe, the line of dots now appearing as a dark transverse band with bright borders. As contraction proceeds the shaft of the muscle-rod tends to, and ultimately disappears, leaving an appearance of alternate dark and light stripes; the former however are in this case due to the enlarged juxtaposed extremities of the rods, the latter on the other hand being mainly due to the accumulation of the ground-substance in the intervals between their shafts. An examination of minute oil-globules imbedded in gelatine shows clearly that they give the appearance under the microscope of dark spots with a brilliant surrounding, and several side by side produce the effect of a bright band. From many considerations it can be shown that the bright transverse bands in muscle are similarly produced by the juxtaposition of the rod-heads, among which are the following:—1. When the rod-heads are smaller the bright bands are narrower. 2. When the rod-heads have become merged with the shafts in full contraction, the bright transverse stripes entirely disappear. 3. When in contraction the rod-heads enlarge and encroach on the shaft, their bright borders accompany them and encroach on the dim substance, so that at last all appearance of dimness becomes entirely obliterated, the bright borders becoming blended in the middle. 4. The part of the muscle-rod where the head joins the shaft, is rendered indistinct by the brightness around the rod-head; whereas if this brightness were inherent in the ground substance, this part of the rod would stand out all the darker by the contrast. 5. The appearance of a transverse section is corroborated; for in this case the rod-heads are seen so close together that the optical effect of any one would become merged into those of its neighbours: consequently the whole of the intermediate substance would appear bright; and this is actually found to be the case. 6. The fact that both the dim and the bright substance of resting muscle appear doubly refracting, would indicate that they are of the same nature.
Article PDF
Rights and permissions
About this article
Cite this article
On the Structure of Striped Muscular Fibre . Nature 7, 489 (1873). https://doi.org/10.1038/007489a0
Issue Date:
DOI: https://doi.org/10.1038/007489a0