414 HANDBOOK OF PHYSIOLOGY. 



If the shocks, however, be repeated at very short intervals, being 15 

 per second for the frog's muscle, but varying in each animal, the muscle 

 contracts to its utmost suddenly and continues at its maximum contrac- 



FIG. 290. Tracing of a double muscle-curve. To be read from left to right. While the muscle 

 was engaged in the first contraction (whose complete course, had nothing intervened, is indicated 

 by the dotted line), a second induction-shock was thrown in, at such a time that the second contrac- 

 tion began just as the first was beginning to decline. The second curve is seen to start from the 

 first, as does the first from the base line. (M. Foster.) 



tion for some time and the lever rises almost perpendicularly, and then 

 describes a straight line (Fig. 292). If the stimuli are not quite so 



FIG. 291 . Curve of tetanus, obtained from the gastrocnemius of a frog, where the shocks were 

 sent in from an induction coil, about sixteen times a second, by the interruption of the primary 

 current by means of a vibrating spring, which dipped into a cup of mercury, and broke the primary 

 current at each vibration. 



rapid the line of maximum contraction becomes somewhat wavy, indi- 



FIG. 292. Curve of tetanus, from a series of very rapid shocks from a magnetic interrupter. 



eating a slight tendency of the muscle to relax during the intervals be- 

 tween the stimuli (Fig. 291). 



