THE MUSCULAR TISSUE. 



1109 



the fibre the appearance of being made up of a bundle of fibrillae, which have been 

 termed sarcostyles or muscle-columns; and if the fibre is hardened in alcohol, it 

 can be broken up longitudinally and the sarcostyles separated from each other 

 (Fig. 639, A). The reticulum, with its longitudinal and transverse meshes, is 

 sar co plasm. 



If now a transverse section of a muscular fibre is made, it 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 trans- 

 parent series of sarcoplasm (Fig. 639, B, >). 



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 Figs. 638 and 639 appears as a mere alternation of 

 dark and light bands, is resolved into the appearance seen in Fig. 640, which shows 

 a series of broad dark bands, separated by light bands, which are divided into two 

 by a dark dotted line. This line is termed Krause s membrane (Fig. 642, K), 

 because it was believed by Krause to be an actual membrane continuous with 



FIG. 640. Portion of a medium-sized human muscular 

 fibre. Magnified nearly MOD diameters. B. Separated bun- 

 dles of fibrils, equally magnified, a. a. Larger, and b. b, 

 smaller collections, c. still smaller, d. d. The smallest 

 which could be detached. 



FIG. 641. Part of a striped muscular fibre 

 of the water-beetle, prepared with absolute 

 alcohol. Magnified 300 diameters. (Klein 

 and Noble Smith.) a. Sarcolemma. 6. 

 Membrane of Krause ; owing to contrac- 

 tion during hardening, the sarcolemma 

 shows regular bulgings. At the side of 

 Krause's membrane is the transparent lat- 

 eral disk. Several nuclei of muscle-cor- 

 puscles are shown, and in them a minute 

 network. 



the sarcolemma, and dividing the light band into two compartments. It is now 

 more usually regarded as being due to an optical phenomenon, from the light 

 being reflected between disks of different rofrangibility. In addition to the mem- 

 brane of Krause, fine clear lines may be made out, with a sufficiently high power, 

 crossing the centre of the dark band ; these are known as the lines of Hensen 

 (Fig. 642, H). 



Formerly it was supposed by Bowman that a muscular fibre was made up of 

 a number of quadrangular particles, which he named sarcous elements, joined 

 together like so many bricks forming a column, and he came to this conclusion 

 because he found that under the influence of certain reagents the fibre could be 

 broken up transversely into disks, as Avell as longitudinally into fibrillae (Fig. 

 639, B). But it is now believed that this cross-cleavage is purely artificial, and 

 that a muscular fibre is built up of fibrillse and not of small quadrangular 

 particles. 



Assuming that this is so, we have now to consider a little more in detail the 

 minute structure of these longitudinal fibrilla;, or sarcostyles, as they are termed. 

 Perhaps there are few subjects in histology which have received more attention, 



