80 



TETANUS. 



[Boon i. 



If the frequency of the shocks be still further increased, as in 

 Fig. 16, the rise due to the combination of contraction will be still 

 more rapid, and a smaller part of each contraction will be visible 

 on the curve. 



FIG. 16. MUSCLE-CUEVE. SINGLE INDUCTION SHOCK REPEATED STILL MORE RAPIDLY. 



In each of these three curves it will be noticed that the 

 character of the curve changes somewhat during its development. 

 The change is the result of commencing fatigue, caused by the 

 repetition of the contractions, the fatigue manifesting itself by an 

 increasing prolongation of each contraction, shewn especially in a 

 delay of relaxation, and by an increasing diminution in the height 

 of the contraction. Thus in Fig. 14 the contractions quite distinct 

 at first, become fused later; the fifth contraction for instance is 

 prolonged so that the sixth begins before the lever has reached 

 the base line ; yet the summit of the sixth is hardly higher than 

 the summit of the fifth, since the sixth though starting at a higher 

 level is a somewhat weaker contraction. So also in Fig. 15, the 

 lever rises rapidly at first but more slowly afterwards, owing to an 

 increasing diminution in the height of the single contractions. In 

 Fig. 16 the increment of rise of the curve due to each contraction 

 diminishes very rapidly, and though the lever does continue to 

 rise during the whole series, the ascent after about the sixth 

 contraction is very gradual indeed, and the indications of the 

 individual contractions are much less marked than at first. 



Hence when shocks are repeated with sufficient rapidity, it 

 results that after a certain number of shocks, the succeeding im- 

 pulses do not cause any further shortening of the muscle, any further 

 raising of the lever, but merely keep up the contraction already 

 existing. The curve thus reaches a maximum, which it main- 

 tains, subject to the depressing effects of exhaustion, so long as the 

 shocks are repeated. When these cease to be given, the muscle 

 returns to its natural length. 



When the shocks succeed each other still more rapidly than 

 in Fig. 16 the individual contractions, visible at first, may become 

 fused together and wholly lost to view in the latter part of the 

 curve. When the shocks succeed each other still more rapidly 



