PROTEINS 



555 



fibrils exhibit distinct rodlet birefringence (Stubel, 1925). It follows 

 from this that the fibrils are not uniform in structure, but are of the 

 class of rodlet composite bodies. Boehm and Weber (1932) produced 

 composite bodies of this kind artificially by injecting myosin solutions 

 into water. The resulting filaments displayed the same optical proper- 

 ties, both qualitatively and quantitatively, as the Q sections of the 

 myofibrils (Weber, 1934). It is surprising to find how well the 

 measured birefringence agrees with that calculated from Wiener's 

 formula (see p. 84), for the assumptions of Wiener's composite 

 bodies are hardly applicable to hydrophilic micellar systems. Above 

 all, the theory requires that there should be a well-defined phase 

 boundary between the rods and the imbibition liquid, which there 



cannot be with a swellable protein which adds on 

 water molecules to its macromolecular chains. A 

 further assumption, which is more to the point in 

 this case, is that the submicroscopic rodlets have 

 practically unlimited length. Weber, it is true, 

 assumes a particle length of only 500 A and Wor- 

 SCHITZ (1935) has X-ray evidence for lengths up 

 to 2050 A, but no reliance can be placed on X-ray 

 determinations of particle length with dimensions 

 beyond 500 A (see Frey-Wyssling 1937a, p. 376). 

 It may therefore be assumed with equal justice that 

 the optically identified rodlets are bundles of 

 primary valence chains of unknown length which 

 run parallel through the myofibrillae. 



X-ray analysis. X-ray analysis gives us some in- 

 formation about the inner structure of elementary 

 fibrils. Myosin filaments produce the same X-ray 

 diagram as relaxed muscles (Boehm and Weber, 

 1932), which proves the identity between the 

 fibrillar substance and myosin. Model experiments 

 can therefore be carried out with m^^osin films and 

 it is in this way that Astbury and Dickinson 

 (1935 a) found that the X-ray picture of muscle 

 protein corresponds to that of keratin. The a ?^ 

 /3-keratin conversion can be attained by elongation, 

 but in the relaxed muscle it is not the stretched 



Fig. 176. Striated 

 muscle fibres between 

 crossed nicols (by 

 courtesy of Prof. 



W. J. Schmidt, 



Giessen). Wide Q 



sections and narrow, 



weakly luminous Z 



stripes. 



