THE ELECTROMOTIVE PHENOMENA 305 



key. The meniscus will be displaced by the 

 demarcation current. When the meniscus has 

 come to rest, stimulate the nerve with, single and 

 repeated induction currents. 



With each stimulus there will be a negative va- 

 riation (action current) of the demarcation current. 



When the number of stimuli per second passes 

 a certain point, which differs with different in- 

 dividuals, the hitherto separate excursions of the 

 meniscus will be fused, and a gray blur will 

 appear at the end of the vibrating column. 

 Movements of this rapidity may of course be 

 studied by photographing them on sensitive paper 

 moving rapidly enough to draw the fused image 

 out into a line in which its component oscilla- 

 tions are each distinct, or they may be observed 

 directly by the stroboscopic method. 



The Action Current in Tetanus ; Stroboscopic 

 Method. 1. If a piece of thin black paper about 

 1 cm. square is fastened vertically on the end of 

 the electro-magnetic signal lever, and the signal 

 placed in the primary circuit of the inductorium 

 arranged for tetanizing currents, the piece of 

 paper will move each time the primary current 

 is made or broken by the vibrating hammer of 

 the inductorium. The movement is so rapid 

 that the paper seems stationary and a gray haze 

 appears on its upper and lower border. 

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