SINGLE CONTRACTION OR TWITCH. 165 



circuit of the induction machine short-circuited, and with 

 wires to go to the binding screws on the platform of the 

 moist chamber on the myograph (Fig. 62). [The muscle may 

 be caused to contract either by stimulating it directly in 

 which case the electrodes are made of thin wires and 

 merely pushed through the two ends of the gastrocnemius 

 or indirectly through the nerve. It is convenient to use 

 the latter method (Lesson XXIX., 3).] 



(c.) Make a nerve-muscle preparation, leaving the lower 

 end of the femur in connection with the gastrocnemius, and 

 cut away the tibia and fibula. With the point of a sharp pair 

 of small scissors make a small hole in the tendo Achillis, and 

 insert in it a hook like the letter S, made by bending a pin. 

 Manipulate the nerve with a camel's-hair pencil. Arrange 

 the preparation in the moist chamber by fixing the femur in 

 the muscle clamp, and by means of a stout ligature thread 

 attach the hook in the tendo Achillis to the writing-lever under 

 the ebonite or wooden stage of the moist chamber. See that 

 the muscle or ligature goes clear through the hole in the stage, 

 and that the hook does not catch on anything. Adjust the 

 height of the muscle clamp, so that the writing-lever is 

 horizontal. Place the nerve over the electrodes, and cover 

 the whole preparation with the glass-shade lined on three 

 sides with moist blotting-paper. Load the lever near where 

 the muscle is attached to it by a weight of 20 grammes 

 or thereby, and make the lever itself horizontal. Arrange 

 the point of the lever so that it writes on the cylinder. The 

 writing-style on the tip of the lever may be made of very 

 thin copper foil or parchment paper, fastened on to the 

 lever with sealing-wax or telegraph composition. 



8. According as the recording surface is stationary, or moving 

 when the muscle contracts and raises the lever, either a vertical 

 line or a curve will be made upon the paper. In the latter case 

 the form of the curve will vary with the velocity of the drum. 

 Arrange experiments for both. 



A. Begin with the recording cylinder stationary. 



(a.) Push the secondary coil far away from the primary, 

 open the key in the secondary circuit, and make and break 

 the primary circuit. There may be no contraction. Close 

 the secondary circuit key. 



