THE BIOLOGY OF THE CELL SURFACE 



But in these studies is lack of agreement. According 

 to one view the fibrils arise from cytoplasm which is 

 itself of fibrillar structure; another view maintains that the 

 fibrils arise from cytoplasmic inclusions. The living 

 muscle-cell in tissue-culture often fails to show the structure 

 seen in fixed preparations; according to many investigators 

 cross striations do not appear until after the cell is fixed. 

 I venture the following suggestion as to the cross-striations 

 in the muscle-cell. 



The young striated muscle-cell, like that of smooth 

 muscle, possesses ectoplasmic prolongations. The pro- 

 longations arising first fuse at their outer tips and thus 

 form a membrane so that this region of the ectoplasm has a 

 palisade-like structure. Repetition of this process through- 

 out the length of the cells forms fibrils (the membranes) 

 crossed by ectoplasmic prolongations. 



Beyond I shall show that the surface of the fertilized egg 

 of the sea-urchin is made up of radial filaments covered by 

 a thin membrane. My conception of the striated muscle- 

 fibril has its origin in this fact. Since other cells than eggs 

 show such projections, it is not too extreme to suggest that 

 the embryonic muscle-cell also possesses such. The slender 

 muscle-cells have the inherent capacity to build up succes- 

 sively striated fibrils by reconstitution of their surface. 

 The sea-urchin's egg builds one such surface layer which 

 remains inseparably bound to the egg-cell; the muscle-cell 

 builds many such surfaces. 



Also on other grounds my conception of the origin of the 

 cross-striated muscle-fibril is not so far-fetched as it may 

 seem. In the first place, the generally accepted doctrine of 

 muscle-activity emphasizes the role of surface in the 

 phenomenon of its contraction. The fact that in the 

 contraction process, in one stage, oxygen is utilized, is 

 evidence indicating a surface-reaction. Moreover, the 

 shape of the muscle-fibre strongly supports the theory that 



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