374 



MYOLOGY 



sr/a 



' 



found to be marked by alternate light and dark bands or striae, which pass trans- 

 versely 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 2/x. If the surface be carefully 

 focussed, rows of granules will be de- 

 tected at the points of junction of the 

 dark and light bands, and very fine 

 longitudinal lines may be seen run- 

 ning through the dark bands and 

 joining these granules together. By 

 treating the specimen with certain 

 reagents (e. g., chloride of gold) fine 

 j^ ! f 5; lines may be seen running transversely 

 5 (^ 5?/ between the granules and uniting them 

 igjj? gg together. This appearance is believed 

 BT ^JJS! to be due to a reticulum or network 

 nq R /]i5i 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 longitu- 

 dinally and the sarcostyles separated 

 from each other (Fig. 375.) The retic- 

 ulum, with its longitudinal and trans- 

 verse meshes, is called sarcoplasm. 



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 con- 

 sisting of the transversely divided sarcostyles, surrounded by transparent sarco- 

 plasm (Fig. 373). 



/4 BB [ 



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 6, b, smaller 

 collections, c. Still smaller, d, d. The smallest which could 

 be detached. 



S.R 



S.E. 



FIG. 376. Diagram of a sarcomere. (After Schafer.) 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. 



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 



