Henry Gray (18251861). Anatomy of the Human Body. 1918.
found to be marked by alternate light and dark bands or striæ, which pass transversely across the fiber (Fig. 374). When examined by polarized light the dark bands are found to be doubly refracting (anisotropic), while the clear stripes are singly refracting (isotropic). The dark and light bands are of nearly equal breadth, and alternate with great regularity; they vary in breadth from about 1 to 2μ. If the surface be carefully focussed, rows of granules will be detected at the points of junction of the dark and light bands, and very fine longitudinal lines may be seen running through the dark bands and joining these granules together. By treating the specimen with certain reagents (e. g., chloride of gold) fine lines may be seen running transversely between the granules and uniting them together. This appearance is believed to be due to a reticulum or network of interstitial substance lying between the contractile portions of the muscle. The longitudinal striation gives the fiber the appearance of being made up of a bundle of fibrils which have been termed sarcostyles or muscle columns, and if the fiber be hardened in alcohol, it can be broken up longitudinally and the sarcostyles separated from each other (Fig. 375.) The reticulum, with its longitudinal and transverse meshes, is called sarcoplasm.
FIG. 375 A. Portion of a medium-sized human muscular fiber. Magnified nearly 800 diameters. B. Separated bundles of fibrils, equally magnified. a, a. Larger, and b, b, smaller collections. c. Still smaller. d, d. The smallest which could be detached. (See enlarged image)
In a transverse section, the muscular fiber is seen to be divided into a number of areas, called the areas of Cohnheim, more or less polyhedral in shape and consisting of the transversely divided sarcostyles, surrounded by transparent sarcoplasm (Fig. 373).
FIG. 376 Diagram of a sarcomere. (After Schäfer.) A. In moderately extended condition. B. In a contracted condition. k, k. Membranes of Krause. H. Line or plane of Hensen. S.E. Poriferous sarcous element. (See enlarged image)
Upon closer examination, and by somewhat altering the focus, the appearances become more complicated, and are susceptible of various interpretations. The transverse striation, which in Fig. 374 appears as a mere alternation of dark and light bands, is resolved into the appearance seen in Fig. 375, which shows a series of broad dark bands, separated by light bands, each of which is divided into two