THE MUSCULAR TISSUES 



low magnification and even in living muscle fibres. When examined 



under higher magnification, after teasing, or in thin sections, the 

 fibril bundles can be seen to consist of nu- 

 merous still finer fibrils, the ultimate fibrillw 

 (sarcous element of Bowman, sarcostyle of 

 Schafer). These ultimate fibrillae are also 

 seen to consist of alternate light and dark 

 disks. When examined under polarized light 

 the dark disks are found to be anisotropic or 

 doubly refracting, the light disks isotropic 

 or singly refracting. 



The alternate light and dark disks are so 

 disposed within the muscle cell that the 

 corresponding disks of adjacent fibrillse lie in 

 the same transverse plane. This arrangement 

 produces alternate light and dark composite 

 disks whose diameter corresponds with that 

 of the muscle cell. These larger alternate 

 light and dark disks, each composed of the 

 corresponding portions 

 of innumerable ultimate 

 fibrillae, give rise to an 

 appearance of transverse 

 striation which is so 



readily visible under either low or high mag- 

 nification as to become the most prominent 



characteristic of this type of muscle cell. 



Regarding the minute structure of the ulti- 

 mate fibrillse, there is still much discussion. 



That the alternate light and dark disks are 



more than mere optical illusions is evidenced 



by the fact that they react differently to 



stains, notably to gold chlorid. Bisecting 



the middle of the dark disk, Hensen in 1868 



described a fine light line, Henseri*s line, and 



it is possible by the action of certain reagents, 



e. g., acids, alkalis, and artificial gastric juice, 



to produce transverse cleavage of the muscle 



cell along this line (Ranvier *). 



z h 



FlG. 67. A BIT OF A STRI- 

 ATED MUSCLE FIBRE 

 SEEN IN LONGITUDINAL 

 SECTION. 



The alternate light and 

 dark cross striations are 

 well shown, ft, light line, 

 Hensen's line, in the mid- 

 dle of the dark disk Q. 

 z, dark line, Krause's 

 membrane or Dobie's line, 

 in the middle of the light 

 disk. Hematein. x 1200. 

 (After Bohm and von 

 Davidoff.) 



FlG. 68. A SMALL POR- 

 TION OF A MUSCLE 

 FIBRE OF A CRAB 

 SHOWING BEGINNING 

 SEPARATION INTO FI- 

 BRILS. 



Drawn from a photo- 

 graph, x 600. (After 

 Schafer.) 



* Traits technique d'histologie. 



