THE MUSCULAR TISSUES. 63 



upon the other). After treatment with alcohol, the fibres of striped 

 muscle readily split up lengthwise into delicate bundles, which, with 

 care, may be subdivided to such an extent that the resulting threads 

 embrace in their width only a single row of alternating light and 

 dark elements. These ultimate fibrillae were formerly considered 

 by Kolliker as the normal elements of the fibre ; the dark prisms of 

 these fibrillae correspond to the sarcous elements, which were 

 regarded by Bowman as the component units of muscular tissue. 

 The transverse cleavage of the fibre following the action of diluted 

 mineral acids, on the other hand, has been upheld as representing 

 the natural division. According to Krause, the fibre is divided 

 through the light bands by a number of transverse partitions con- 

 tinuous with the sarcolemma ; these assumed septa appear as delicate 

 broken lines the membranes of Krause and are identical with 

 the intermediate disks already mentioned. Adopting this view, the 

 fibre is composed of numerous thin zones or contractile disks, 

 each of which embraces the dark dim band in its centre and half of 

 the light stripe at either end. Each contractile disk is further sub- 

 divided by vertical partitions extending between the neighboring 

 membranes of Krause, thus forming in every disk a row of com- 

 partments or muscle-caskets. The portion of the dim band con- 

 tained within each muscle-casket has been regarded as itself being 

 composed of a series of thin prisms of contractile substance the 

 muscle-rods. 



After renewed critical study of the subject, Rollett has presented 

 a view regarding the structure of voluntary muscle which not only 

 offers the most plausible solution of this difficult problem, but is, 

 likewise, in harmony with the history of the development of the 

 tissue. According to this theory, the muscular tissue is composed 

 of the highly specialized, darker, anisotropic contractile substance, 

 and the relatively passive, lighter, semi-fluid, isotropic sarcoplasm. 

 The contractile substance is arranged as delicate spindles, the appo- 

 sition of whose thicker parts produces the dim transverse disk seen 

 under medium amplification ; at either end the spindle is prolonged 

 as an extremely thin thread, which terminates in a minute sphere or 

 bead ; the apposition of these beads in the transverse row gives rise 

 to the appearance of the interrupted line constituting the inter- 

 mediate disk, or Krause 1 s -membrane. The darker anisotropic sub- 

 stance forms, therefore, numbers of continuous contractile fibrillae, 

 which extend in parallel bundles the entire length of the fibre ; all 

 the remaining interfibrillar space within the sarcolemma is filled with 

 the lighter sarcoplasm, which appears faintly granular in preserved 

 tissue, but is, probably, almost fluid during life. On comparing this 

 description with the usual appearances presented by striated muscle, 



