CHANGE OF FORM IN MUSCLE DURING ACTIVITY 133 



least some circumstances, are stimulated by the constant current 

 to quite analogous rhythmical activity. As a rule, however, the 

 constant current only produces a single contraction when it is 

 closed, and eventually when it is opened also (make and break 

 twitch), in striated muscle, both with 'direct or indirect (via nerve) 

 excitation. Interrupted currents have exactly the same effect 

 under certain conditions. 



Bernstein (20) was the first to observe that with a given 

 frequency (about 900 per sec.), and moderate intensity, induction 

 currents led into the frog's sciatic produced a single brief 

 "twitch" of the gastrocnemius, a so-called "initial twitch," 

 instead of tetanus ; this is more apparent in the most rapid 

 interruptions of the primary circuit, grows weaker with diminish- 

 ing frequency of stimulation, and disappears entirely below a 

 certain limit (200 to 300 stimuli per sec.) The phenomenon 

 occurs with both direct and indirect excitation of curarised 

 muscle. According to Griinhagen (21) and Engelrnann (22) 

 there is occasionally a " final twitch " at the close of the tetanus 

 also, corresponding with the opening twitch of the constant 

 current. The investigation of the effects of very high stimula- 

 tion-frequencies on muscle (and nerve) often leads to contra- 

 dictory results, because the application of electrical stimuli of 

 great rapidity presents great technical difficulties, where complete 

 uniformity in strength and order of succession is required. 

 Neither the application of sliding contacts, nor mercury closure, 

 is in this respect sufficiently trustworthy. Even Kronecker's 

 "acoustic current interrupter" (14), in which the longitudinal 

 vibrations of a magnetised iron rod, produced by friction, set up 

 induction currents in a wire coil, fails, according to Both (23), 

 at very high frequencies (over 4000 vibrations). Both (Lc.) has 

 recently employed the microphone, and obtained reliable electrical 

 stimuli of high frequency, which were also regular and perfectly 

 under control. Pipes of different pitch were blown by means of 

 a gas motor, and a dry cell, equal to one Leclanche, was intro- 

 duced into the primary circuit. With indirect excitation of a 

 frog's gastrocnemius (from the nerve) Both found that tetanus 

 disappeared when 5000 stimuli per sec. were sent in from a pipe 

 of 2500 vibrations, with a given strength of the Blake micro- 

 phone. The limit with direct excitation of the muscle lay under 

 similar conditions about 300 stimuli lower. V. Kries sue- 



