128 THE MYOGRAPH. 



5- The Curve Of TetanilS. Arrange the apparatus (as directed in 

 Section I. 2) for single induction shocks. Introduce into the primary circuit 

 a reed which automatically makes and breaks the circuit twenty times in a 

 second. Prepare and fix the muscle according to either of the methods 

 described above. On closing the key of the primary circuit for ten seconds, 

 the muscle is tetanized and the curve inscribed on the cylinder (see p. 56). 



Arrange the induction apparatus for faradization (see Section I. i,b), and 

 repeat the preceding observation. 



6. The Time-Relations of a Muscular Contraction. 



I. By noting the time required for a sufficient number of revolutions of the 

 recording cylinder and accurately measuring its circumference, the rate of 

 movement of the recording surface may be determined, and thereby the 

 time-value of the records known. 2. A more direct method is to write 

 simultaneously under the tracing the oscillations of a tuning-fork of which 

 the vibration-rate is known. For this purpose the tuning-fork may be 

 made to inscribe its vibrations directly, or (more conveniently) it may 

 be introduced into a battery circuit, so as to interrupt it at each vibra- 

 tion. An electromagnetic writer (chronograph) is introduced into the same 

 circuit ; it vibrates synchronously with the fork, and reproduces its motions 

 on the cylinder. Record a curve of single contraction, using the " stretcher," 

 and fix the recording cylinder on the quick axis. Mark the point of 

 excitation by bringing the trigger of the cylinder very slowly into 

 contact with the lever of the key. Measure the distances from the point, 

 (i) to the beginning of the curve, (2) to its maximum, and (3) to its close, 

 and determine their value by either of the methods given above. 



7. Measurement of the Period of Latent Stimulation and of 



the Rate of Propagation in Nerve, by the Pendulum Myograph. 



Preparation of the Apparatus. Cover the glass plate smoothly with paper, 

 smoke its surface as before, and fix it to the pendulum. Arrange the 

 "trigger" and the "catch "so that the pendulum when detached from the 

 former just catches on the latter. Test the instrument by taking tracings 

 with a tuning-fork vibrating 100 times a second, on the smoked paper, when 

 the pendulum is moving at several different velocities (the velocity varying 

 with the positions of the trigger and catch). Arrange the electrical apparatus 

 for single shocks as in Sect. I. 2, including in the primary circuit one of the 

 keys of the myograph. Prepare the gastrocnemius as in Sect. II, I. Fix 

 the femur firmly to the cork table, pass the ligature round the pulley and 

 attach it to the lever, adjusting the spiral spring to a suitable strength. Take 

 great care that no part of the apparatus touches the glass plate, as the pen- 

 dulum swings. Arrange the lever very carefully, so that when it is brought 

 into position by the rotating handle it writes on the smoked surface. Observe 

 that the glass plate is so adjusted that the lever at first touches it lightly, but 

 presses more strongly as the plate swings past. Catch the pendulum with 

 the trigger, see that everything is in order the keys closed, the lever in its 

 position, the electrodes under the nerve, etc. On liberating the pendulum, a 

 muscle curve is inscribed on the smoked surface. Withdraw the lever from 

 its writing position, bring the pendulum back past the key, close the latter, 

 keeping it closed by firm pressure of the finger, allow the pendulum to rest 

 against it, bring the lever into the writing position, and make a mark on the 



