142 



THE STRUCTURE AND ACTION OF "STRIATED" MUSCLE FIBRE. 



By O. W. TiEGS, D.Sc, 

 Zoology Department, University of Adelaide. 



[Read May 10, 1923.] 



Plates XI. to XIV. 



So numerous have been the investigations on the structure and action of 

 striated muscle tissue, and so well do our general ideas on the subject appear 

 to be established to-day, that a re-examination of the whole question may appear 

 superfluous. Nevertheless, observations which I have been making recently 

 have led me to conclude that many of our accepted ideas are quite erroneous, 

 and I shall not hesitate to discuss the subject once more. 



Historical Introduction. 



Among those who have investigated the structure of striated muscle are to 

 be mentioned Leeuwhenhoek, Bowman, Dobie, Kolliker, W. Krause, Hensen, 

 Merkel, Engelmann, Schafer, Rutherford, Retzius, Rollett, Ramon y Cajal, 

 McDougall. 



Leeuwhenhoek is said to have regarded the striations as being in the form 

 of a spiral thread wound around the outside of the cylindrical fibres. Bowman 

 (1840) investigated the structure of. the fibres carefully, and regarded the dark 

 striations as closely packed discs stretching across the fibres ; he recognized 

 also the presence of muscle fibrillae. Nine years later Dobie observed a very 

 faint line between the striations, to which Rutherford (1897) gave the name 

 Dobie's Line. This "line" was shown by the investigations especially of 

 Schafer (1873) to consist of a very delicate membrane which stretched right 

 across the fibre (Krause's Membrane), on either side of which a layer of minute 

 dim dots are to be seen ; these dots, together with Krause's membrane, are to 

 be looked upon as constituting Dobie's line. Rutherford, on the other hand, 

 regarded Krause's membrane as being confined to the fibrils, and it was, accord- 

 ing to him, not to be looked upon as a complete membrane stretching across 

 the fibres. Schafer's opinion has prevailed, and is, I am convinced, the correct 

 one. 



In 1868 Hensen described the pale stripe often seen passing through the 

 striation (Hensen's Line). By some authors (e.g., McDougall and Merkel) 

 this line was regarded as a membrane stretching across the fibre like Krause's 

 membrane. Rutherford, however, denies this view, and it is not accepted to-day. 



Bowman, in his original account, had regarded the transverse discs as 

 composed of minute particles closely arranged side by side so as to produce the 

 disc, and less closely united behind one another to form the fibrils. To KoUiker 

 (1851) we owe the modern conception that the fibrils are the primary com- 

 ponents of the fibres, the arrangement of their individual striations to form 

 the discs of the fibre being secondary. To a structureless substance lying between 

 these fibrils, Rollet has given the name Sarcoplasma. 



Meanwhile Schafer (1891) working with the sarcostyles of the wing muscles 

 of insects, structures which he regarded as highly differentiated fibrillae, has 

 actually been able to observe internal dift'erentiation of these delicate structures, 

 minute tubules being observed in the region of the striation when examined with 

 very high powers. As late as 1897, however, Rutherford wrote : "The finest 

 structure of the fibrils is beyond the reach of the microscope, so that the secret 

 of contraction will ever remain hidden." 



