STIMULATION OF NERVES. 503 



easily produced when the positive pole or anode is next the 

 muscle. Sometimes in particular conditions of the nerve, and 

 with certain strength of stimulation, a making tetanus also occurs, 

 but more rarely and only when the negative pole is next the 

 muscle. 



When a constant current, such as we get directly from a 

 Daniell cell, is used, that part of the nerve between the stimu- 

 lating points through which the current passes is found not to be 

 equally affected throughout its entire length, but one single point 

 is stimulated whence the impulse spreads. This may be the point 

 where either of the poles is in contact with the nerve ; and fur- 

 ther, a different pole starts from the stimulus, according as the 

 circuit is made or broken. With a making shock the stimulation 

 takes place at the negative pole or cathode, and with a breaking 

 shock at the positive pole or anode. That is to say, the point 

 where the current leaves the nerve is affected at the make, and 

 the point where the current enters the nerve is affected at the 

 break of the current. 



It has also been found that, other things being equal, the mak- 

 ing shock is a more powerful stimulus than the breaking shock, 

 i. e., a weak current will sooner cause a contraction when the 

 circuit is made than when it is broken. 



This remarkable fact, that the impulse starts from the anode in 

 a breaking shock, is proved by means of the breaking tetanus just 

 alluded to. It has been found that when the positive pole or 

 anode is next to the muscle, the breaking tetanus lasts longer and 

 is stronger than when the anode is placed at a greater distance 

 from the muscle than the cathode ; and further, when the anode 

 is beyond the cathode section of the nerve in the intrapolar region, 

 during stimulation the tetanus stops it at once, because the point 

 from which the stimulus comes is thereby cut off from the muscle. 

 Section has no effect if the anode be next the muscle, the tetanus 

 proceeding in a normal way, only the inactive pole being cut away 

 from the muscle. That the stimulus occurs at the cathode in a 

 making current may also be demonstrated by the fact that it takes 

 a certain measurable time for the impulse to travel along the 

 nerve. If, then, the cathode be placed far from the muscle and 



