202 



PRACTICAL PHYSIOLOGY. 



[xxxv. 



one is insulated. The axis of the drum carries a horizontal (adjust- 

 able) arm or " striker " carrying a platinum wire which touches a 

 wire fixed on a support on the insulated binding screw. Thus every 

 time the drum revolves a shock is induced, and always at the sajue 

 moment, so that successive shocks can be recorded on the same 

 abscissa and the moment of stimulation can be found at once. 



3. Simple Muscle-Curve with Crank-Myogi*aph and Automatic 

 Break. — Apparatus required. — (1) Recording- drum moving at a 

 fast rate (about 50 cm. per second); (2) crank-myograph ; (3) 

 chronograph vibrating 100 times per second ; coil ; keys. 



F16. 120.— Arrangement for analysis of Muscle-Curve by means of Crank-Myograph (JO 

 with " Automatic Break " Arrangement in Primary Circuit. S. Striker on axis of D 

 cylinder; P.C. Primary, and S.C. Secondary circuits; T.C. TimL-ciicuit witli E.M. 

 Electro-magnet ; I.S. liisulated support in P.C. 



(a.) Arrange the apparatus as in fig. 120. The cylinder (D) is 

 placed in the primary circuit. Wlien the horizontal arm or striker 

 (S) fixed to the vertical spindle touches the upright, the primary 

 circuit is made and broken and induction shocks are induced in the 

 secondary circuit. Select a break shock, i.e., when the make is not 

 yet effective. The vertical support (I.S) is insulated from the 

 base of the drum support. 



(b.) Short-circuit the secondary current, arrange a nerve-muscle 

 preparation on a crank-myograph (M), place the nerve on the 



