THE HIGHER ANIMAL TISSUES.

51

therefore, the temptation would rather be to class them with the tissues which we see produced by the transformation of the connective tissues. Yet this would at the present moment be still rather a venturous undertaking.

FIG. 23.

Amongst all the forms of which we have here to treat, the elements of muscle have generally been regarded as the most simple. If we examine an ordinary red muscle (I do not say a voluntary one, inasmuch as in the heart also we meet with fibres of the same form) we find it to be essentially composed of a number of cylinders, for the most part of equal thickness (primitive fasciculi [fibres]), which on a transverse section are seen to have a cylindrical form, and on which we at once perceive the well-known transverse striæ, that is, broad lines which generally run transversely through the fasciculus with a somewhat wavy outline, and are almost as broad as the intervals that separate them. In addition to this transverse striation we also see, especially when certain modes of preparation have been adopted, striæ following a longitudinal direction, and these, indeed, in some preparations preponderate to such a degree, that the muscular fasciculus appears to be striated almost exclusively in this direction. If now we add acetic acid, there are forthwith disclosed immediately beneath the sheath, and now and then also more towards the centre, nuclei which are tolerably large,

Fig. 23. A group of primitive muscular fasciculi [fibres]. a. The natural appearance of a fresh primitive fasciculus, with its transverse striæ (bands or discs). b. A fasciculus gently acted upon by acetic acid; the nuclei stand out distinctly, and in one of them two nucleoli are visible, whilst in another the division is complete. c. A fibre acted upon more strongly by acetic acid; the contents are swollen up at the end, so as to protrude from the sheath (sarcolemma). d. Fatty atrophy. 300 diameters.

and mostly contain large nucleoli in greater or less number. In this manner, therefore, after we have cleared up the internal substance by the application of acetic acid, we again obtain an appearance which reminds us of the original cellform; and there has been the greater tendency to regard the whole of a primitive fasciculus as having sprung from a single cell, because, according to the view which was formerly entertained, the individual primitive fasciculi of every muscle were thought to extend from the point of origin to that of insertion, and were therefore held to be as long as the muscle itself. This latter supposition has, however, been shaken by investigations which were set on foot in Vienna, under Brücke's direction, by Rollet, for he demonstrated that in the course of muscles the ends of primitive fasciculi, are to be seen running into points, so that a primitive muscular fasciculus would comport itself like a large fibrecell (Fig. 105, A). These ends fit one into the other, and, according to this, the length of a primitive fasciculus would by no means correspond to the whole extent of the muscle.

On the other hand, I must remark, that observations have been made in different quarters quite recently, which are rather of a nature to throw doubts upon the uni-cellular nature of these elements. Leydig regards them as rather containing a series of cells of a smaller kind, between which the contractile substance is lodged, his idea being based upon the circumstance that every nucleus (Figs. 23,b,c; 24, B) is enclosed in a special elongated cavity.1 In

This cavity Leyden supposes to be lined by a membrane, and therefore really to constitute a cell (connective-tissue corpuscle). The nuclei of every primitive fasciculus would, therefore, according to this view, be the nuclei of connective-tissue corpuscles, and the contractile substance, lying between these, would be equivalent to the intercellular substance of ordinary connective tissue. The nuclei here alluded to are the ordinary nuclei of muscle, as seen in the figs. quoted above and must not be confounded with the awl-shaped bodies represented in fig. 24, C, lying between the fibrils; for, though these bodies look like nuclei, they are really, according to Leydig, portions of the divided processes of some of his connective-tissue corpuscles.-From a MS. note by the Author.

TRANSVERSELY STRIATED MUSCLES.

53

discussions respecting these ultimate elements of muscle, extremely difficult relations are involved, and I for my own part must confess that, however much I am inclined to admit the uni-cellular nature of the primitive fasciculi, I am still too familiar with the peculiar appearances in their interior not to be obliged

FIG. 24.

we have to do with a

a

structure in which an external membranous sheath (sarcolemma) and contents

are to be distinguished. In the latter, acetic acid causes nuclei to shew themselves, and, when they (the contents) are in their natural condition, the peculiar transverse and longitudinal striation may be recognised in them. This striation is altogether internal, and not external. The membrane in itself is perfectly smooth and even; the transverse striation belongs to the contents, which, when seen in a mass, form the red substance of the muscle.

Now it is this substance which has the property of contractility indubitably inherent in it, and even varies in appearance according to its state of contraction, becoming broader

A.

Fig. 24. Muscular elements from the heart of a puerperal woman. Peculiar spindle-shaped cells precisely like the fibre-cells of the pulp of the spleen, probably belonging to the sarcolemma and set free in teasing out the preparation. a. Crescentically curved cell, somewhat flat at one end, viewed on its surface. b. A similar one, seen in profile, with flat nucleus. c, d. Cells, the nuclei of which lie in a hernial protrusion of the membrane. e. A similar cell, viewed on its surface, with its nucleus, as it were, lying upon it. B. A primitive fasciculus, without its sheath (sarcolemma), with distinct longitudinal fibrils and large, roundish nuclei, of which one contains two nucleoli (incipient partition). C. A primitive fasciculus, which has been teased asunder and slightly cleared up by acetic acid; besides a divided nucleus, fine, awlshaped, nucleus-like bodies are seen imbedded between the longitudinal fibrils. 300 diameters.

when contracted, whilst the intervals between the individual transverse bands become somewhat narrower, so that a change in the arrangement of its minutest constituents takes place, and this, as seems probable from the investigations of Brücke, not merely in the case of its physical molecules, but also in that of its visible anatomical constituents. Brücke, namely, by examining muscle by polarized light, has discovered different optical properties in the individual layers of substance-in those which compose the transverse striæ and those which form the intervening mass. On the adoption of certain methods of preparation, every primitive muscular fasciculus appears to be made up of plates or discs of a different nature, piled up one above another, and these in their turn to be entirely composed of minute granules (Bowman's sarcous elements). In reality, however, the contents of a primitive fasciculus consist of a certain number of fine, longitudinal fibrils, every one of which contains minute granules corresponding in position to the transverse striæ or apparent discs of the primitive fasciculus, and held together by a pale, intervening substance. Now, since a considerable number of primitive fibrils lie in apposition side by side, there arises, in consequence of the symmetrical position of the little granules, this very appearance of discs which really do not exist. In proportion to the activity of the muscle these parts assume an altered position with regard to one another; during contraction the granules are approximated, whilst the intervening substance becomes shorter and, at the same time, broader.

Compared with this, the structure of the smooth, organic, or, although this is a less expressive term, involuntary muscular fibres, appears much more simple. On examining any part of those organs in which smooth muscular fibres are contained, we find in the majority of cases, first of all, just as was the case with the transversely striated muscles, little

SMOOTH MUSCLES.

FIG. 25

55

fasciculi―as, for example, in the muscular coat of the urinary bladder. Within these fasciculi, upon further investigation, a series of distinct elements can be distinguished, of which a certain number, six, ten, twenty, or more, are held together by a common connective substance. According to the notion which universally prevailed until quite recently, every one of these elements was analogous to the primitive fasciculus of striped muscle. For as soon as we succeed in separating these fasciculi of smooth muscle into their more minute constituents, we find their ultimate elements to consist of long, spindle-shaped cells, which usually con

According to the

tain a nucleus in their centre (Fig. 5, 6). view on the contrary, which, especially in consequence of the impulsion given by Leydig's investigations, has quite lately begun to be mooted in various quarters, we should have to regard the bundle, in which a whole series of fibre-cells is contained, rather as analogous to a transversely striated primitive fasciculus. Until, however, this point has been satisfactorily settled, I consider it advisable and more in accordance with known facts to regard each fibre-cell as the equivalent of a primitive fasciculus. Should, however, any change of opinion shortly occur, you will now at any rate be prepared for it.

Fig. 25. Smooth muscular fibres from the parietes of the urinary bladder. 4. Fasciculus still coherent, out of which at a, a single, isolated fibre-cells protrude, whilst at b their simple divided ends appear. B. A similar fasciculus after being treated with acetic acid, whereby the long and narrow nuclei have become evident. a and b, as above. 300 diameters.