ii CHANGE OF FORM IN MUSCLE DURING ACTIVITY 109 



battery current. In either case the waves of contraction are, as 

 it were, fixed in their passage through the muscle, and a more or 

 less prolonged, nearly uniform tetanus ensues, or, as it is better 

 expressed in the absence of almost any evidence of discontinuity 

 in the contraction, there is a " tonic " shortening in all the parts 

 of the entire muscle. 



As already shown by Bezold and Fick, different forms of 

 contraction may be distinguished in the veratrin muscle, one 

 of the commonest being that in which the peculiar tonic, per- 

 sistent contraction is preceded by a more or less pronounced 

 and rapid introductory 

 twitch. As shown 

 above, there is a rapid 

 maximum contraction at 

 the moment of excita- 

 tion, followed immedi- 

 ately by a considerable 

 extension, succeeded in 

 its turn by a second 

 slow contraction which 

 only gradually yields 

 to relaxation (Fig. 46). 



Indications of this 

 characteristic contrac- 



are rarely absent, FIG. 46. Make -twitch of veratrinised Frog's sartorius (1 

 if the Prepar- Daniell). The characteristic tonic contraction is preceded 



by a rapid initial twitch. (Biedennami.) 



ation is immersed for a 



long period in dilute salt solution. As Fick showed, the initial 

 twitch cannot be explained by indirect excitation of the muscle from 

 the intra-muscular nerves the subsequent persistent contraction 

 only being due to direct excitation of the muscle for the same 

 curves are exhibited after previous curarisation. The phenomenon 

 may presumably be related to the fact first observed by Grlitzner, 

 of the constitution of muscle out of two morphologically and func- 

 tionally different kinds of fibres, corresponding to the red and 

 pale (sluggish and quick) muscles. This view receives support 

 from the fact that the same double-topped curves of contraction 

 are not infrequent under other conditions, e.g. local treatment 

 with Na. 2 C0 3 , or even in perfectly normal frog's muscle. In 

 sartorius itself Griitzner finds it to be the rule. If the veratrin 



