83 



from one another by the sarcoplasm (protoplasm), which 

 varies in quantity in different kinds of fibres. 



In stained preparations the muscle fibre reveals 

 alternate light and dark cross-striations. At its centre, 

 each light band is interrupted by a transverse line 

 (Krause's membrane). There is also a transverse line 

 stretching across the middle of the dark band (Hensen's 

 line). The latter is only seen with dilficulty. Each 

 portion of a fibril between two adjacent Krause's 

 membranes is known as a " sarcomere." 



Haycraft's* experiments led him to believe that the 

 cross striations are due to regularly-occurring varicosites, 

 and some of the preparations made in the course of the 

 present work appear to show this. It is doubtful whether 

 this structure (even if admitted) is alone sufficient to 

 account for the fact that the cross-striations seen in fresh 

 tissue are accentuated under the action of various 

 staining reagents. It is highly probable, as suggested by 

 Schafer, that the cross striation of the fibrils is due to the 

 heterogeneous nature of the latter. 



An examination of the fresh muscles of a crab reveals 

 the interesting fact that as in the vertebrates some of 

 the muscles are of a darker colour than others. Sections 

 across the muscle fibres show that, generally speaking, the 

 " dark " muscles have much more sarcoplasm than the 

 " light " ones. Hence Knoll distinguished between 

 plasmic (dark) and aplasmic (light) fibres. Biedermannf 

 has shown that there is a definite relationship between the 

 amount of sarcoplasm present in a fibre and the nature of 

 the work performed by the fibre. He has, furthermore, 

 stated that " the elements of those muscles which serve 



* Haycraft, J. B. " Cause of Striation of Voluntary Muscular 

 Tissue," Q.J.M.S., Vol. XXI (1881). 



t Biedermann, W. Electro-physiologij, Vol. I. 



