50 TETANIC CONTRACTIONS. [BOOK i. 



When however repeated shocks are given it is found that the 

 height of each contraction is rather less than the preceding one, 

 and this diminution becomes more marked the greater the number 

 of shocks. Hence 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, in the usual way, at first very rapidly, and then 

 more slowly, to its natural length. When the shocks do not succeed 

 each other too rapidly, the individual contractions may readily be 

 traced along the whole curve, as is seen in Fig. 7, where the 

 primary current of the induction-machine was repeatedly broken 

 at intervals of sixteen in a second. When the shocks succeed 

 each other more rapidly, the individual contractions, visible at first, 



FIG. 8. TETANUS PBODUCED WITH THE OBDINABY MAGNETIC INTEBEUPTOB OF AN IN- 

 DUCTION-MACHINE. (Eecording surface travelling slowly.) To be read from left to right. 



The interrupted current being thrown in at a the lever ris t es rapidly, but at b the 

 muscle reaches the maximum of contraction. This is continued till c, when the 

 current is shut off and relaxation commences. 



may become fused together and lost to view as the tetanus con- 

 tinues and the muscle becomes tired. 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 the single contractions. The curve then described by 

 the lever is of the kind shewn in Fig. 8, where the primary current 

 of an induction-machine was rapidly made and broken by the 

 magnetic interrupter, Fig. 9. The lever, it will be observed, rises 

 at a after the latent period (which is not marked), first rapidly, 

 and then more slowly, in an apparently unbroken line to a maxi- 

 mum at about 6, maintains the maximum so long as the shocks 

 continue to be given, and when these cease to be given, as at c, 

 gradually descends to the base-line. This condition of muscle, 

 brought about by rapidly repeated shocks, this fusion of a number 

 of simple spasms into an apparently smooth, continuous effort, is 

 known as tetanus, or tetanic contraction. The above facts are most 

 clearly shewn when induction-shocks, or at least galvanic currents 

 in some form or other, are employed. They are seen, however, 

 whatever be the form of stimulus employed. Thus in the case of 



