Ill 



ELECTRICAL EXCITATION OF MUSCLE 



177 



detected even at a slow rate of the recording surface, but is 

 much plainer with a quick movement. According to Tigerstedt 

 (2) the process of each make contraction must be of a tetanic 

 character, since the corresponding curves are much more ex- 

 tended than in twitches provoked by induction currents (Fig. 

 72). But it is needless to say that there is not necessarily- 

 any true " tetanus," i.e. contraction resulting from summation. 

 From these facts alone we may conclude that besides the intensity 

 of current, its duration in the muscle also affects the strength 

 of excitation (or contraction), while this appears yet more 

 plainly from corresponding experiments on sluggish muscles, 



FIG. 72. 1-8, Contraction curves on excitation of the muscle by single induction shocks ; 9-19, con- 

 traction curves (make twitches) on exciting with the constant current (" tetanus " character). 



(Tigerstedt.) 



where the magnitude of effect as dependent upon the duration of 

 the excitation appears to be in exact inverse ratio with the 

 mobility of the particles of an irritable substance. The extra- 

 ordinarily small and often negative effect of single induction 

 shocks on many protozoa, and on vegetable protoplasm, is well 

 known, while in smooth muscle such short stimuli, if they act 

 at all, first take effect at a high intensity, although they seldom 

 or never fail to excite the rapidly twitching striated fibres. 

 This is remarkably well seen on every relaxed (a-tonic) pre- 

 paration from the adductor muscles of anodonta (3). From 

 these, as was said above, it is easy to obtain a preparation as 

 susceptible to electrical excitation as the frog's sartorius (Fig. 73). 



N 



