32 PHYSIOLOGY CHAP. 



If one muscle of a lightly veratrinised animal (frog or toad) 

 is detached, fixed to the myograph, and stimulated with an 

 induction shock, the resulting curve will be very different from 

 that of the normal twitch (in Fig. 23), as the rapid contraction is 

 followed by a long contracture which slowly diminishes. 



Fick endeavoured to explain this phenomenon by assuming 

 that the rapid primary contraction depends on the indirect 

 excitation of the muscle transmitted by the intramuscular nerves, 

 and the subsequent contracture on the direct excitation by the 

 poison. But this interpretation is contradicted by the fact that 

 it is possible to obtain the same form of curve from animals that 

 have previously been curarised. Griitzner proposes another 

 explanation, and suggests that the rapid primary and slow 

 secondary contraction depend on two distinct species of fibres 



Fie:. 23. Gontracture of gastrocnemius muscle of veratrinised toad, produced by simple break 

 shock from an induced current. (Bottazzi.) The tracing shows that the veratrin contracture 

 is preceded by an ordinary contraction, which is suddenly interrupted at the commencement 

 of the relaxation. Time tracing in half-seconds. 



(pale and red, rapid and torpid) in the muscle. This hypothesis 

 is contradicted by the later observations of Carvallo and Weiss, 

 according to which both the pale muscles and the red exhibit 

 the characteristic veratrin contracture. The most probable 

 explanation is that of Eottazzi, who regards the coexistence of a 

 rapid and a slow contraction as due to the presence in the 

 muscle fibres of two distinct contractile materials, endowed with 

 different degrees of excitability anisotropous and isotropous 

 substance. 



The hypothesis that the singly refracting substance of the 

 sarcoplasrn is capable of causing positive and negative variations 

 in the tone of the muscle, independently of the simultaneous 

 rhythmical excitation of the doubly refracting substance, explains 

 the phenomenon discovered by Fano in the auricular musculature 

 of Emys europea (Vol. I. p. 319), which exhibits rhythmical 

 oscillations of tone, on which the ordinary cardiac rhythm is 

 superposed. The plain muscles of the oesophagus in toad, fowl, 



