198 PRACTICAL PHYSIOLOGY. [XXXIV. 



electrodes, moist chamber and lever (or crank-myograph), moist 

 blotting-paper, stout ligatures, hook, pins, lead weight (20 grams). 



(a.) Cover the drum with glazed paper, smoke it, and arrange it 

 to move slowly. 



(b.) Arrange the apparatus : DanielFs cell and a mercury key 

 in the -primary circuit, the secondary circuit short-circuited, and 

 with wires going to the binding screws on the platform of the 

 moist chamber on the myograph (fig. 116). [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 XXXII.).] 



(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 an S-shaped 

 hook, made by bending a pin. Arrange the preparation in the 

 moist chamber by fixing the femur in the muscle clamp, and by 

 means of a stout thread attach the hook in the tendo Achillis to 

 the writing-lever. See that the muscle or ligature goes clear 

 through the hole in the stage, and that the hook does not catch on 

 anything. 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 either directly or by means of a 

 scale -pan near where the muscle is attached to it by a weight of 

 about 20 grams, and make the lever itself write horizontally on the 

 cylinder. The writing-style on the tip of the lever may be made 

 of very thin copper foil or parchment paper, fastened to the lever 

 with sealing-wax or telegraph composition. 



As here arranged the primary circuit is made and broken by 

 hand. 



According as the recording surface is stationary or moving 

 when the muscle contracts and raises the lever, either an upward 

 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. 



A. Simple twitch with the recording cylinder stationary. 



By this arrangement one registers only the lift or height of the 

 contraction, and its relation to the strength of the stimulus ; 

 yielding minimal and maximal contractions. A light (isotonic) 

 lever is chosen, such as will amplify the movement 6-8 times, 

 while the weight to be lifted is such that the tension of the 

 muscle is about 8-10 grams. 



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

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



