ELEMENTARY EXPERIMENTAL PHYSIOLOGY 25 



ciently rapid rate ; the rate of rotation should not be less than 

 20 cm. per sec. Adjust the writing points to touch the smoked paper 

 lightly, and with the Du Bois key open, and the fork vibrating, let the 

 drum make one revolution and no more. The curve of the muscular 

 contraction and the time below it in y^ths of sec. will be recorded 

 (Fig. 32). Close the Du Bois key, remove the tuning-fork, but do not 

 alter the position of the base of the stand carrying the myograph. 

 With the writing point of the lever accurately on the abscissa line of 

 the muscle curve let the drum revolve so as to complete a base line 

 beneath the actual curve corresponding to the muscular contraction. 

 With the writing point still on the base line, rotate the drum by hand 

 until the striker just touches the naked wire. At this position of the 



FIG. 32. Single contraction of gastrocnemius in response to a maximal make 

 shock. Muscle loaded with lever and 30 grms. at axis of lever ; actual load on muscle, 

 6grms. Magnification, 5. Temp., 15 C. Time marker, 100 per sec. (A.P.B.) 



drum a maximal make induction-shock was sent into the nerve ; with 

 the finger on the lever make the writing point describe a vertical arc, 

 which cuts the time-tracing below and the abscissa line above. In the 

 same way, by rotating the drum by hand, vertical arcs are drawn 

 through the muscle-curve and time-tracing at the three following 

 points : (1) the point at which the curve leaves the base line, (2) 

 the highest point of the curve, and (3) the point at which the curve 

 regains the base line. 



It will be noted that, during the single revolution of the drum, the 

 primary circuit has not only been made but also been broken again 

 by the striker leaving the naked wire. The nerve has consequently 

 received a maximal make and then a maximal break shock, but has only 

 responded by a contraction to the first; for, owing to the rapid 

 rotation of the drum, the second stimulus has reached the muscle 

 too soon after the first for the muscle to be able to respond (see Re- 

 fractory period of muscle, p. 42). If, however, the drum is revolving 

 but slowly, the second stimulus may follow the first after a sufficient 

 interval of time for the muscle to partly respond to it. This leads 



