VOL. 4 (1950) MORPHOLOGY IN MUSCLE AND NERVE PHYSIOLOGY 7I 



properties of muscle. So far as the morphological evidence is concerned, Perry, Reed, 

 AsTBURY, AND Spark^^ have shown by X-ray and electron microscope studies that the 

 changes which occur when ATP is added to actomyosin is an intermolecular syneresis, 

 the contraction occurring in a direction normal to that which characterizes muscle con- 

 traction. Moreover, there is no evidence from X-ray results for the existence of two 

 distinct states of the "auxones". Upon contraction the large-angle pattern indicates 

 a change from an alpha to a poorly defined, disoriented beta configuration. Efforts to 

 obtain a characteristic small-angle pattern from contracted muscle have thus far met 

 with failure. What httle electron microscope evidence bears on this point suggests that 

 the 400 A axial period shows a continuous change in value with change in fibre length 

 rather than two distinct states. 



However valuable partial systems and models may be from the biochemical view- 

 point, it is evident that, in the investigation of structural mechanism which is charac- 

 teristic of muscle, final answers will be obtained by observation of nothing less complex 

 than the muscle fibre itself. 



There is no reason to doubt that the combination of X-ray diffraction and electron 

 microscopy will be equal to the task of disclosing the molecular changes which occur in 

 contraction. The small-angle X-ray analysis is particularly promising and may be 

 expected in the near future to portray the main features of the lattice of Bear's Tjq^e II 

 protein. The more detailed structure at smaller separations, involving the configurations 

 of polypeptide chains in relaxed and contracted muscle seems more difficult of unique 

 solution unless more diffraction data can be obtained at large angles. 



An electron microscope investigation of the extra-filamentous structures of the 

 striated myofibril, including the materials concerned in the "reversal of striation", the 

 Z membranes and the binding material which connects filaments to each other and to 

 the sarcolemma laterally, offers much promise. However, primary interest attaches to 

 the detailed structure within the filament and the changes of this structure with con- 

 traction. As compared with paramyosin the task of the electron microscopist will be 

 considerably more exacting because of the smaller spacings involved. Obviousty, at this 

 level of size the most critical judgement of image quality and of optical artifacts will 

 be required. 



NERVE CONDUCTION 



The problem of nerve conduction contrasts strikingly with that of muscle con- 

 traction as regards the contributions of morphology. This is due to the fact that the 

 changes whicht occur in a nerve fibre when an impulse is conducted are far more subtle 

 than those occurring during contraction and also to the fact that chemical characteri- 

 zation of nerve fibre constituents, particularly the proteins, is almost completely lacking. 

 Until about the turn of the century the extensive histological literature emphasized 

 primarily the neurofibrils which were regarded by many as the substratum of impulse 

 conduction. In its most stimulating form this hypothesis visualized the interface be- 

 tween axoplasm and neurofibril as the locus of the electro-chemical changes which 

 underlie impulse propagation^^. Bethe's^^ demonstration of a difference of stainability 

 of neurofibrils under the anode and cathode of a polarizing current, due to the presence 

 in axoplasm of a hypothetical "fibrillary acid", attracted little attention though the 

 phenomenon seems quite genuine and has some renewed interest in the light of recent 

 References p. 76JJJ. 



