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GENERAL PHYSIOLOGY OF JIDBCLH AND x KRVE . 103 



muscle-cells fibres as they are called, arranged side by side in bundle, the 

 whole being bound together by a fine connective-tissue network. Each n 

 fibre consists of a very delicate elastic sheath, the sarcolemma, which i 

 plete y filled with the muscle-substance. Under the microscope the fib as are 

 seen to be striped by alternating light and dark transverse bands, and on fox- 

 ing the difference in texture which this suggests is found to extend through 

 ibres, i.e. the light and dark bands correspond to little disks of substances 

 of different degrees of translucency. More careful study with a high T >ower 

 shows under certain circumstances other 

 cross markings (see Fig. 36, A), the light 

 band is found to be divided in halves by 

 a fine dark line, Z, and parallel to it is 

 another faint dark line, n, while the dark 

 baud, , is found to have a barely per- 

 ceptible light line in its centre. 



The fine dark lines, Z, which run 

 through the middle of the light bands, 

 were for a time supposed to be caused by 

 delicate membranes (Krause's membrane), 

 which were thought to stretch through 

 the fibre and to divide it into a series of 

 little compartments, each of which had 

 exactly the same construction. Kuehne 

 chanced to see a minute nematode worm 

 moving along inside a muscle-fibre, and 



Observed that it encountered no obstrilC- contracting fibre by ordinary light ; D, contract- 

 , ing fibre by polarized light. 



tion, such as a series of membranes, how- 



ever delicate, would have caused. As it moved, the particles of muscle-sub- 

 stance closed in behind it, the original structure being completely recovered. 

 This observation did away with the view that the fibre is divided into com- 

 partments, but the arrangement shown in Figure 36, A, repeats itself through- 

 out the length of the fibre and indicates that it is made up of a vast succession 

 of like parts. 



Muscle-substance consists of two materials, which differ in their optical 

 peculiarities and their reaction to stains. If a muscle-fibre be examined by 

 polarized light, it is found that there is a substance in the dark bands which 

 refracts the light doubly, is anisotropic, while the bulk of the substance in the 

 light bands is singly refractive, isotropic (B, Fig. 36). The anisotropic sub- 

 stance is found to stain with hffimatoxylin, while the isotropic is not thus 

 stained ; on the other hand, the isotropic substance is- often colored by chloride 

 of gold, which is not the case with the anisotropic. By means of these reac- 

 tions it has been possible to ascertain something as to the arrangement of these 

 substances within the muscle-fibre, though the ultimate structure has not been 

 definitely decided. It appears that the isotropic material is the sarcoplasma, 

 which is distributed throughout the fibre and holds imbedded within it the 



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FIG. 36. schema of histoiogicai structure of 



