82 TETANUS. [BOOK i. 



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 

 impulses 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 

 maintains, 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. 17 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 

 (the second contraction beginning in the ascending portion of 

 the first), it becomes . difficult or impossible to trace out any of 

 the single contractions 1 . The curve then described by the lever 

 is of the kind shewn in Fig. 18, where the primary current of an 



FIG. 18. TETANUS PRODUCED WITH THE ORDINARY MAGNETIC INTERRUPTOR or AN 



INDUCTION-MACHINE. (Recording surface travelling slowly.) 



The interrupted current is thrown in at a. 



induction-machine was rapidly made and broken by the magnetic 

 interruptor, Fig. 5. The lever, it will be observed, rises at a (the 

 recording surface is travelling too slowly to allow the latent period 

 to be distinguished), at first very rapidly, in fact in an unbroken 

 and almost a vertical line, and so very speedily reaches the maxi- 

 mum, which is maintained so long as the shocks continue to be 

 given ; when these cease to be given, the curve descends at first 

 very rapidly and then more and more gradually towards the base 

 line, which it reaches just at the end of the figure. 



This condition of muscle, brought about by rapidly repeated 

 shocks, this fusion of a number of simple twitches into an 



1 The ease with which the individual contractions can be made out depends in 

 part, it need hardly be said, on the rapidity with which the recording surface travels. 



