BY DR. MICHAEL FOSTER. 371 



CHAPTER XXIV. 

 TETANUS. 



1. The Curve of Tetanus. Obs. I. Having arranged 

 the nerve-muscle preparation, etc., in the moist chamber as 

 usual, draw first, if not ready at hand, the curve of a simple 

 muscular contraction, for comparison. 



Then connect the electrodes with the induction machine 

 using the magnetic interrupter ; insert between the secondary 

 coil and the electrodes the marking key with double circuit ; 

 raising the marking key will now allow an interrupted current 

 to fall into the nerve ; on pressing the key down the current 

 will be shut off. 



All being arranged (the slow axis of Se'cretan's instrument 

 will give sufficient speed), allow an interrupted current of 

 very moderate intensity (i. e., the secondary coil hardly, if at 

 all, overlapping the primary with a weak battery) to break 

 into the nerve, and in a few seconds shut it off again. 



A curve similar to that shown in fig. 282 will be obtained ; 

 where the plumb line in drawn through the first a marks the 

 commencement both of the stimulation and contraction (the 

 speed not being sufficient to show the latent period), and the 

 line in 1 through the second a marks the end of the stimulation, 

 and ?w s the end of the contraction. 



It will be seen that the curve rises at first very rapidly, 1 

 afterwards more slowly, and speedily reaches a maximum, which 

 it maintains during the whole time of the stimulation. Upon 

 the cessation of the stimulus at wi 2 , the curve at once falls, at 

 first very rapidly, but afterwards more slowly, and in its later 

 phases very slowl}'. 



If the stimulus is allowed to act upon the muscle for more 

 than a few seconds, the curve begins to decline, even while the 

 stimulus is still acting; but, even after very prolonged stimu- 

 lation, the cessation of the stimulus is indicated by a sharp 

 fall in the curve. 



Tetanus from an ordinary interrupted current is a continued 

 contraction rapidly reaching a maximum, continuing (within 

 limits) in that condition so long as the current is passing, and 

 followed by a gradual relaxation upon the current being cut 

 off- 



1 In the figure the curve does not rise rapidly enough. 



