140 



THE TISSUES. 



diameter), forming \^\& fibril bundles or muscle-columns of Kolliker. In 

 the muscle-columns the fibrils are so placed that the larger segments 

 fall respectively in the same plane. (See Fig. 96.) The same disposi- 

 tion of the fibrils prevails in all the numerous muscle-columns form- 

 ing a muscle-fiber, and all the muscle-columns bear such a relation 

 to each other that the larger segments of the fibrils fall in the same 

 plane. The semifluid, interfibrillar substance, the sarcoplasm, pene- 

 trates between the fibrils of the muscle-columns and separates these 

 from each other and from the sarcolemma. In fresh preparations the 

 substance forming the fibrils appears somewhat darker and dimmer,' 

 while the sarcoplasm appears clearer. The sarcoplasm is found in 

 greater abundance between the muscle-columns than between the 

 fibrils in the columns. The sarcoplasm between the muscle-columns 

 appears in the form of narrower or broader lines, parallel to the 

 long axis of the muscle-fibers, giving the cross-striated muscle-fiber 

 also a longitudinal striation. The sarcoplasm between the muscle- 

 columns is seen to best advantage in cross-sections of the muscle- 

 fiber. Here it appears in the form 

 of a network inclosing the mus- 

 cle-columns. Thus, we have in 

 a cross-section slightly darker 



, & . J .. 



areas, the cross-sections of the 

 muscle-columns, known as Cohn- 

 heinfs fields or areas, separated 

 by the network of sarcoplasm. 

 (Fig. 98.) 



Fig. 99- From a striated muscle of 

 man ; obtained by teasing ; X ' 2O - h> A 

 median disc lying in the transverse disc Q; 

 z, the membrane of Krause borders above 

 and below on the light isotropic discs. 



Fig. 100. From a cross-section 

 through the trapezius muscle of man, 

 showing dark fibers rich in protoplasm, 

 and light fibers containing very little pro- 

 toplasm (after Schaffer, 93, II) : d, Dark 

 fibers ; a, light fibers ; b and c, transitional 

 fibers from light to dark. 



In figure 99 is shown a portion of a striated muscle-fiber of 

 man very highly magnified. The larger and darker transverse disc 

 (Q) formed by the larger segments of fibrils is divided by a light 

 line (H), Hensen's median disc; the clearer band, largely isotropic 

 substance, is divided by a dark line, the membrane of Krause, z. 



After a prolonged treatment with 98^. alcohol the muscle-fibers 



