452 MUSCLE PHENOMENA. 



contraction, and its myogram is shown in Fig. 259. This is a 

 simple muscle-curve. 



latent Period. The moment that the stimulus reaches the 

 muscle is represented by a in the illustration, but the upward 



FIG. 259. Myogram from gastrocneruius muscle of frog ; beneath, the time is re- 

 corded in 0.005 second : a, moment of excitation ; b, beginning of contraction ; c, 

 height of contraction ; d, end of contraction (Lombard). 



curve begins at 6. So that between these events there is an 

 interval of 0.006 second, as shown by the lowest line, in which 

 the curves are made by a time-marker. This interval is the latent 

 period. At 6 the curve begins rapidly to rise, then more slowly, 



FIG. 260. Superposition of contractions: 1 is the curve when only one stimulus 

 is thrown in ; 2, when a second stimulus acts at the time when curve 1 has nearly 

 reached its maximum height (Stewart). 



when it reaches its highest point, c. Then, as the muscle begins 

 to relax, there is a downward curve until the line is reached from 

 which the curve started, this line being the abscissa ; the descend*- 

 ing curve shows that the relaxation is at first rapid, then becomes 

 slower, and occupies a longer time than the contraction. From 

 a to 6 occupies about 0.006 second ; from b to c, about 0.05 second ; 

 from c to d, about 0.07 second. Helmholtz, in his experiments 



