GENERAL PHYSIOLOGY OF MUSCLE-TISSUE. 



FIG. 1 6. MUSCLE-FIBER OF A RABBIT. 

 a. Dark band. b. Light band. 

 c. Intermediate line. n. Nucleus. 



to all changes of form the sarcous substance undergoes. Beneath 

 the sarcolemma there are several nuclei surrounded by granular 

 material. Each fiber also presents a sejiej_j2LJ^ariSYers_ .bands 

 alternately dim anoM^right which 

 give to it a^striated appearance. 

 If the bright bands are examined 

 with high magnifying powers, each 

 one is seen to be crossed by a fine 

 dark line which at the time of its 

 discovery was regarded as the 

 optic expression of a membrane 

 attached laterally to the sarco- 

 lemma. It has since been re- 

 solved into a row of granules 

 (Fig. 16). 



The muscle-fiber also presents 

 a longitudinal striation which in- 

 dicates that it is composed of 

 finer elements placed side by side, 



termed fibrillas. The fibrillae extend throughout the entire length 

 of the fiber, though they are not of uniform thickness (Fig. 1 7). That 



portion of the fibril corresponding 

 in position to the dim band is 

 thick, prismatic, or rod-like in 

 shape, and termed a sarcostyle; 

 that portion corresponding in po- 

 sition to the bright band is ex- 

 tremely thin and narrow and pre- 

 sents at its middle a slight enlarge- 

 ment or granule. The fibrillae arei 

 embedded in a clear transparent! 

 fluid which, from its supposed! 

 nutritive character, is termed ^rj 

 corjlasm^^cThe diminution IXL cali- 

 ber of the fibrillae at different 

 levels permits of the accumulation 



FIG. 17. A. Diagram of arrangement 

 of the contractile substance ac- 

 cording to the view of Rollett; the 

 granular figures represent the con- 



tractile elements, the intervening and ^^ Q & krger amoimt 



light areas the sarcoplasm. 

 Small muscle-fiber of man; the 

 corresponding parts in the two 

 figures are indicated; /, i, /, respec- 

 tively the transverse, the interme- 

 diate, and lateral discs, n. Muscle 

 nuclei. (Piersol.) 



of nutritive material than could 

 otherwise be the case. It is for 

 this reason that the fiber at thes 

 points presents a brighter appear- 

 ance. 



When the muscle-fiber is ex- 

 amined under crossed Nichol prisms, the dim band appears bright 

 and the bright band appears dim against a dark background, indi- 

 5 



