MUSCLE-NERVE. 



XV. SUMMATION OF CONTRACTIONS AND GENESIS OF TETANUS. 



Make a semimembranosus-gracilis muscle preparation. Clamp 

 bony attachment in the muscle clamp. Attach the other end to the 

 muscle lever. Connect muscle up for direct stimulation with the 

 secondary coil of an inductorium, arranged for single shocks. In 

 order that the stimuli may be of equal intensity, it is well to use 



B 



FIG. 13. Cut-out Key. B t Battery ; P, primary coil of inductorium ; S, secondary 

 coil; a, &, and c, ct, metal strips ; i and 2, metal clip contacts to complete circuit be- 

 tween a, b, and c, d ; 3, crank to revolve clip contacts i and 2. Contacts revolved in 

 direction of arrow. Contact at a, b, is made an instant before that at t, d. The 

 secondary circuit is therefore short-circuited before the primary is made. The 

 secondary is opened before the primary is broken. Hence the make shock is cut out. 

 Connect S with c, d, and P with a, t>, to cut out break shock. 



some form of cut-out key, so that either the make or break shock 

 may be eliminated (see Fig. 13). 



1. Arrange key to give only break stimuli. Stimulate muscle 

 with one break shock. Note form of contraction curve and height 

 of contraction. The drum should be revolving at medium high 

 speed. 



2. Allow the muscle to rest for a moment. Stimulate again, and, 



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