ELEMENTARY EXPERIMENTAL PHYSIOLOGY 41 



injure the nerve. (8) Cut through the tibia below the knee (Fig. 35, 

 4), and thus remove it and the foot. 



C. Bring the Preparation on to the Frog-board (Fig. 36). 



(1) Lay the muscle and nerve upon a piece of blotting paper 

 thoroughly saturated with 0*75 percent. NaCl solution and placed on 



6V tensors 



FIG. 35. 



the cork plate of the frog-board. (2) Attach the tendon by a thread 



and hook or clip to the middle hole of the short limb of the crank 



lever. (3) Fix the femoral end of the muscle to the cork plate by 



a pin passed through the 



femur, so that the lever is 



supported in a horizontal 



position by the thread (Fig. 



37) . (4) Put a small weight, 



5 grms., on the lever just 



clear of the stand. (5) See 



that the lever is not resting 



on the screw-pin below it. 



(6) Place the nerve upon 



the electrodes, which may 



be fixed to the cork by a 



pin. (7) Make and break 



the current by moving the 



drum with the hand in one 



direction so as not to dis- 



place the striker, and move 



the secondary coil out till 



breaking alone causes a 



contraction. FIG. 36. Myograph stand with crank lever. 



D. Take Trace. 



(1) Now bring the point of the lever lightly against the smoked 

 surface of the drum, (a) pointing it in the direction in which the drum 

 travels, (6) and taking care that the movable base-piece of the frog-board 

 is pushed thoroughly home, so that the lever may be swung off and 

 replaced with exactly the same pressure on the drum when required. 

 (2) With the finger raise the lever to see that it marks properly, and 

 if necessary adjust the lever by twisting the attachment so that it 

 moves in the vertical plane. (3) With the key in the secondary 

 circuit closed start the drum, and, when it is revolving steadily, 



