CH. XII.] 



CURRENTS OF REST AND ACTION. 



first current the current of rest, and the second current, the 

 current of action ; the change in direction is indicated by the 

 expression negative variation ; this means that the current of 

 action is in the opposite direction to the current of rest, and 

 therefore lessens or neutralises it. The word negative is there- 

 fore used in its arithmetical, not its electrical sense. Du Bois 

 Reymond explained this by supposing that a muscular fibre is 



Fig. 170. Diagram of the currents in a muscle prism. (Du Bois Reymond.) 



built up of molecules, each of which is positive in the centre 

 and negative at both ends. So when a muscle is cut across, 

 a number of the negative ends of these molecules is exposed. 

 On contraction the difference between the centre and ends of each 

 molecule is lessened, and the resultant effect on the whole muscle 

 (made up of such molecules) is similar. 



There is no doubt about the facts as described by Du Bois 

 Reymond. We now adopt, however, an entirely different view of 

 their meaning : in causing this revolution of ideas the principal 

 part has been played by Hermann. The new idea is that the 

 so-called current of rest does not exist ; it is really a current 

 produced by injury, and is now generally called a demarcation 

 current : the more the ends of the muscle are injured the more 

 negative they become; and when they are connected to the 

 uninjured centre, a current naturally is set up as described by Du 

 Bois Reymond. If a muscle is at rest and absolutely uninjured it 

 is iso-electric ; that is, it gives no current at all when two parts of 

 it are connected together by a wire. 



Since Du Bois Reymond's researches, the electrical changes 

 which occur during a single twitch have been studied also, and 

 before we can understand the " negative variation " of tetanus, 

 it is obviously necessary to consider the electrical variation which 



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