GENERAL PHYSIOLOGY OF MUSCLE-TISSUE 



53 



The muscle-fiber also presents a longitudinal striation which indicates 

 that it is composed of finer elements placed side by side, termed fibrillae. 

 The fibrillae extend throughout the entire length of the fiber, though they 

 are not of uniform thickness. That portion of the fibrilla correspond- 

 ing in position to the dim band is thick, prismatic, or rod-like in shape, and 

 termed a sarcostyle; that portion corresponding in position to the bright 

 band is extremely thin and narrow and presents at its middle a slight en- 

 largement or nodule. The fibrillae are embedded in a clear transparent fluid 

 which, from its supposed nutritive character, is termed sarcoplasm, or 

 interfibrillar substance. The diminution in caliber of the fibrillae at different 

 levels would permit of the accumulation and storage of a larger amount of 

 this nutritive material than could otherwise be the case. It is for this 

 reason that the fiber at these points presents a brighter appearance. 



When the muscle-fiber is examined 

 by polarized light, the dim band ap- 

 pears bright and the bright band appears 

 Him against a dark background, indicat- 

 ing that the former is doubly refracting 

 or anisotropic, the latter singly refracting 

 or isotropic. 



FIG. id A. Diagram of 

 arrangement of the contrac- 

 tile substance according to 

 the view of Rollett; the 

 granular figures represent 

 the contractile elements, the 

 intervening light areas the 

 sarcoplasm. B. Small 

 muscle-fiber of man, the 

 corresponding parts in the 

 two figures are indicated; 

 /, *, /, respectively the trans- 

 verse, the intermediate, and 

 lateral discs, n. Muscle 

 nuclei (Piersol.) 



FIG. 15. MUSCLE-FIBER 

 OF A RABBIT, a. Dark 

 Iraitit b. Light band, c. I n- 



termediaie line, n. Nucleus. 

 (Landois and Stirling) 



