412 HANDBOOK OF PHYSIOLOGY. 



line (I) is that described by the marking-lever, and indicates by a sudden 

 drop the exact instant at which the induction-shock was given. The 

 lower wavy line (t) is traced by a vibrating tuning-fork, and serves to 

 measure precisely the intervals of time occupied in each part of the con- 

 traction. 



It will be observed that after the stimulus has been applied, as indi- 

 cated by the vertical line s, there is an interval before the contraction 

 commences, as indicated by the line c. This interval, termed (a) the 

 latent period, when measured by the number of vibrations of the tun- 

 ing-fork between the lines s and c, is found to be about yfoj- sec. The 

 latent period is longer in some muscles than in others, and differs also 

 according to the condition of the muscle, being longer in fatigued mus- 

 cles, and the kind of stimulus employed. During the latent period there 

 is no apparent change in the muscle. 



FIG. 288. Muscle curve obtained by means of the pendulum myograph. s. indicates the exact 

 instant of the induction shock; c, commencement; and m x, the maximum elevation of lever; t> 

 the line of a vibrating tuning-fork. (M. Foster.) 



The second part is the (b) stage of contraction proper. The lever 

 is raised by the sudden contraction of the muscle. The contraction ist 

 at first very rapid, but then progresses more slowly to its maximum, in- 

 dicated by the line m x, drawn through its highest point. It occupies in 

 the figure T fo sec. (c) The next stage, stage of elongation. After 

 reaching its highest point, the lever begins to descend, in consequence 

 of the elongation of the muscle. At first the fall is rapid, but then be- 

 comes more gradual until the lever reaches the abscissa or base line, and 

 the muscle attains its precontraction length, indicated in the figure by 

 the line c'. This stage occupies T |~o second. Very often after the main 

 contraction the lever rises once or twice to a slight degree, producing 

 curves, one of which is seen in Fig. 290. These contractions, due to the 

 elasticity of the muscle, are called most properly (d) Stage of elastic 

 after-vibration, or contraction remainder. 



