STRUCTURE OF MUSCULAR TISSUE. 803 



appear to consist of alternate rectangular light and dark particles, constitut- 

 ing the " sarcous elements" of Mr. Bowman. The dark particles are thicker 

 than the light ones, and in consequence of their being less easily acted on 

 by dilute hydrochloric acid and gastric juice, can be obtained in a detached 

 or separate state after short exposure to the action of either of these fluids. 

 Briicke has described the dark particles as refracting light doubly (anisotro- 

 pous") whilst the clear intervening substance is only singly refractile (isotro- 

 pous). 1 Dr. Martyn, 2 in examining a fortunate specimen of muscular tissue 

 under a very high power (1200 linear), observed large and small sarcous 

 elements to occur alternately, as had previously been described by Busk and 

 Huxley; 3 the smaller one evidently corresponding to the faint transverse 

 line traversing the clear space long ago perceived and described by Dr. 

 Sharpey and the Author, from careful observation of Mr. Lealaud's prepa- 

 rations. 4 Careful accounts of the structure of striated muscle have recently 

 been given by Eugelmanu 5 and by Schiifer. 6 The former observer describes 

 each fibre as being, when fresh, almost perfectly transparent and homogene- 

 ous, but speedily undergoing a kind of coagulation, which is hastened by the 

 addition of any reagent, and results in the appearance of a series of super- 

 imposed disks, varying in their thickness and their action on light. These 

 confer upon the tissue its peculiar striated aspect, and the following Figure 

 (284) exhibits them in a diagrammatic form ; the septal or intermediate disk, 

 z, he describes as resembling a homogeneous membrane, which with sharp 

 focussing forms the darkest stria of the fibre ; water and various reagents 

 make it granular or beady, though the fibre may still retain its contractile 

 power. It is doubly refracting, and its greatest thickness (in Articulata) is 

 0.0008 mm. It is highly elastic i. e., is compressed and extended with 

 difficulty. It corresponds to the septum between two compartments of mus- 

 cular fibre if that view of the structure of muscular fibre be taken. The 

 sarcolemma presents either an annular groove, or an elevation where it is 

 attached to it, and the connection between the two is usually firm. 2. The 

 isotropal layer between the septum and the collateral or secondary disk is 

 almost immeasurably thin. 3. The secondary or collateral disk (?i), Flogel's 

 " granule-layer," has a thickness of 0.002 mm. This is usually separated 

 from the anisotropal substance by a thin layer of isotropal substance, but is 

 sometimes fused with it, as can easily be determined by polarized light, the 

 anisotropal substance then appearing much thinner, since the collateral disk 

 presents but feeble indications of double refraction. It adheres less firmly 

 to the sarcolemma than to the septal disk. In breaking a fibre across me- 

 chanically, the rupture commonly occurs between the collateral and the 



1 Briicke further regards the dark particles as uniaxial positive crystals, having 

 their axes parallel to the direction of the fibres, and as being composed of minute 

 solid doubly-refracting particles, which he terms disdiaclasts. See Strieker's Hum. 

 and Comp. Histology, Syd. Soc. Trans., vol. i, p. 235, 1870. 



2 Beale's Archiv, 1862, p. 227. 



3 Note to Kolliker's Man. of Hum. Histology, Syd. Soc. Trans., vol. i, p. 239. 



4 Dr. Macnamara (Med. Times and Gazette) describes the muscular fibres of the 

 chameleon when examined with the highest powers (-gL) as composed of a sheath of 

 sarcolemma containing two longitudinal flat bands, connected by a spirally wound 

 band, the shadow or the approximation of two coils of which forms the transverse 

 striae. Between the horizontal bands are open spaces, as is shown by their never be- 

 coming stained with carmine. M. Rouget (Brown-Sequard's Journ. de la Physio- 

 logic, and Med.-Chir. Kev. ; see also Comptes Rendus, 1867, pp 1128, 1232, and 

 1276) regards the elementary fibrilla of striated muscles as being a spirally twisted 

 ribbon, of which the coils, ordinarily separated from one another or stretched, ap- 

 proximate on the removal of all exciting and nutritive conditions. 



5 Pfliiger's Archiv, Bd. vii, pp. 33-71. 



6 Philosoph. Transact , 1873, p. 429. 



