170 EXPERIMENTAL PHYSIOLOGY. 



the writing point of the lever from the recording surface. 

 Bring the pendulum back to the detent, adjust the writing- 

 style, close the trigger-key, and keep the secondary circuit 

 short-circuited by closing the du Bois key. Allow the 

 pendulum to swing. This records the abscissa or base line. 



(/) Ascertain the latent period as follows : Bring the 

 pendulum to the detent, short-circuit the secondary current, 

 and withdraw the writing-style as in (e.) Close the trigger- 

 key of the pendulum, and with a finger of the left hand 

 keep it closed. Allow the lever to touch the glass plate 

 in its original position, and with the right hand bring the 

 knife-edge of the pendulum in contact with the trigger-key so 

 as just to open it. Thus a vertical line is inscribed on the 

 stationary plate, which indicates the moment of stimulation. 



(g.) Remove the muscle lever, place the pendulum in the 

 detent, close the trigger-key, take a tuning-fork vibrating, 

 say, 120 or 250 double vibrations per second, and adjust its 

 writing-style in the position formerly occupied by the style of 

 the muscle lever. Set the fork vibrating, either electrically 

 or by striking it. Allow the pendulum to swing, when the 

 vibrating tuning-fork will record the time curve under the 

 muscle curve (Fig. 64, 250 DV). All the conditions must be 

 exactly the same as when the muscle curve was taken. 



(h.) Remove the paper, varnish the tracing, hang it up 

 to dry, and next day measure the tracing. Bring ordinates 

 vertical, a', 6', c', to the abscissa, and measure the " latent 

 period" (Fig. 64, A), the duration of the shortening (B), 

 the phase of relaxation (C), and the contraction remainder. 



Fig. 64. Pendulum Myograph Curve. S, Point of stimulation ; A, latent 

 period ; B, period of shortening, and C, of relaxation. 



2. Spring Myograph (Fig. 65). The arrangements are exactly 

 the same as for the pendulum myograph, the trigger-key of the 

 myograph being placed in the primary circuit. The instrument 

 must be raised on blocks. 



