372 TETANUS. 



Obs. II. Arrange for a single induction coil, but replace the 

 key 6 by the oscillating interrupter (Chap. XIX., sec. XIII.). 

 Use the first or the second axis cf Secretan, and the needle of 

 the interruptor being clear of the mercury, open the key a, 

 and set the cylinder revolving. "When uniformity of speed 

 has been reached, suddenly set the interruptor vibrating, and 

 after some ten vibrations or so have taken place, close the key a. 



The tracing on the cylinder will be a curve of the character 

 shown in fig. 283. 



In general features it resembles the curve, fig. 282. There 

 is the'same rise, maximum, and fall ; but instead of being, as 

 in fig. 282, apparently a simple curve, it is evidently composed 

 of a series of curves. Each of these component curves cor- 

 responds to a contraction caused by a breaking or a making 

 of the primary current through the needle dipping into or 

 coming out of the mercury. It will be seen that the second 

 contraction began before the first was completed, and is, so to 

 speak, placed on the top of it ; in the same way , the third 

 comes on the top of the second, and so on. The amount of 

 rise contributed by each subordinate curve to the total rise is 

 greatest in the first, and goes on diminishing until the maxi- 

 mum is reached. 



By varying the length of the oscillating slip, a series of 

 curves may be obtained, showing the various steps between a 

 series of quite separate contractions, each being completed 

 before the next begins, and one in which (as in the tetanus 

 produced with the magnetic interruptor) the individual con- 

 tractions follow each other so rapidly, that no trace of their 

 separate existence is visible on the recording surface. 



Tetanus really consists of a series of simple muscular con- 

 tractions fused together. 



II. The Effects of Exhaustion. 



Obs. III. Throw a muscle, with the electrodes applied to the 

 muscle itself, into tetanus, with a strong interrupted current. 

 Record the movement on the cylinder. Continue the current 

 for some minutes. The curve will gradually fall from the maxi- 

 mum down to very nearly the abscissa line : but even after 

 very prolonged action, a sudden fall will mark the shutting off 

 the current. 



06s. IV. Send through a muscle a single induction shock of 

 a certain strength. Record the contraction. Then tetanize 

 the muscle by means of the interrupted current for ten or 

 twenty seconds. Apply again the same induction shock as 

 before. There will be either a much slighter contraction than 

 before, or none at all. After waiting some minutes, repeat the 

 shock r.gain. The contraction will now be much nearer its 

 former dimensions. 



