50 ELECTRO-PHYSIOLOGY CHAP. 



(E) lines between (N) and (Z) can no longer be distinguished, as 

 is the case at the outset in the less richly striated fibres. A 

 striking change occurs in the next stage within the (a) system. 

 Instead of the colourless segment (J) two strongly-coloured bands 

 appear, while a clear stripe takes the place of (Z) between them. 

 Eollett denotes the former by (/), and the latter by (Z f \ since 

 they are undoubtedly derived from (J) and (Z\ as appears particu- 

 larly from their behaviour in polarised light the dark (J') like 

 the light (e7) is singly refracting, while the clear (Z f ) like (Z) is 

 doubly refractile. When, as sometimes happens before the 

 last stage is completed, the segments (J'} are not yet quite dark, 

 the segments (Z r ) on the other hand not quite light, so that 

 they resemble each other, the muscle-fibres meeting at the points 

 of the contraction wave exhibit most indistinct cross-striation ; 

 this is the so-called homogeneous stage of earlier authors, form- 

 ing the transition to the system (J 1 } and (Z' + J f ), which again 

 represents the commonest transition to the series of bands in the 

 completely contracted muscle. While the clear (Z f ) is disappear- 

 ing between the dark (J 7 ), these in their turn melt into the 

 " contraction-band " (0), as described by Nasse, which is highly re- 

 fracting, very dark, and intensely blue, in the haematoxylin 

 reaction. It obviously corresponds with the system (J+Z-\-J) 

 or (J+N+E + Z+E+N+J} of the relaxed and resting fibres, 

 from the transformation of which it has arisen. 



The changes within the (metabolous) segments (Q h Q) are 

 at first less striking, and the contraction is also smaller. Later on 

 the band clears up, the difference between the darker (Q) and (Ji) 

 grows less and less, and finally a dark, ill-defined band (m. Eollett) 

 appears in place of the latter. Rollett denotes the entire series 

 of altered segments (Q k Q) in the contracted fibre by ((/). The 

 transition from relaxation to contraction in a fibre often proceeds 

 much more slowly than in the example described above ; the 

 single stages may extend over several segments of the fibres, an 

 effect which only enhances the clearness of these figures. 



Polarisation phenomena during contraction are not easy 

 to follow on fresh muscle-fibre, but Eollett (22) was able to 

 assure himself of a diminution of the double refractibility, 

 a fact that can also be ascertained from fixed waves of con- 

 traction, and had been previously conjectured by Engelmann (23) 

 (cf. Ebner, 24, p. 233). It is directly apparent from the fact 



