LESSON IV 

 MUSCLE AND NERVE (Continued) 



SINGLE CONTRACTION, SUMMATION AND FUSION OF CONTRACTIONS. 

 TETANUS. INFLUENCE OF CHANGES IN THE STRENGTH OF THE 

 STIMULUS AND LOAD OF THE MUSCLE 



1. Single Contraction or "Twitch." Attach a gastrocnemius muscle 

 to the clamp and the writing lever. Place an electromagnetic signal 

 directly below the writing lever, so that their points come to lie close 

 together and precisely in the same vertical line (ordinate). Fasten a 

 scale pan underneath the writing lever, but in such a way that it cannot 

 interfere with the movement of the lever. Connect the signal in series 

 with the cells and posts 1 and 2 of the indue torium. Adjust the sec- 

 ondary coil to obtain induction shocks of medium strength. Fasten a 

 tuning-fork to a separate stand which is placed to the left of the kymo- 

 graph, so that the pointer of the fork vibrates against the rotation of 





FIG. 18. ELECTROMAGNETIC SIGNAL. (Univ. of Penna. Lab. Outlines.) 



the drum. Raise the drum of the kymograph from its friction-surface 

 by properly adjusting the screw in the top of the rod. 



Let the tuning-fork register its vibrations ( T ^ sec.) directly below 

 the record of the signal. With your left hand then spin the drum once 

 around its axis, and with your right hand close and open the key of 

 the primary circuit. The speed of the drum should be such that the 

 circuit may be made and broken conveniently during a single rotation 

 of the drum. Repeat this experiment a number of times. Place a 

 ruler vertically against the kymograph and draw perpendiculars through 

 the: 



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