140 



THE ELECTRICAL PHENOMENA OF MUSCLE [cH. XII. 



thrown into tetanic contraction, the needle returns more or less 

 completely to the position of rest. 



Du Bois Keymond, who first described these facts, called the 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 therefore used in its arithmetical, 

 not its electrical sense. Du Bois Keymond explained this by sup- 

 posing that a muscular fibre is built up of molecules, each of which 

 is galvanometrically positive in the centre and galvanometrically 



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



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

 of the galvanometrically 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. 



In the foregoing sentence I have employed the rather cumbrous adjectives, 

 galvanometrically positive and galvanomelrically negative, instead of the terms 

 positive and negative which are usually employed by physiologists. 



If we take a Daniel! cell and connect it to a galvanometer, the zinc, as we have 

 seen, is the electro-positive element, and the copper the electro-negative element, 

 but the ends of the wires which connect these metals to the galvanometer have the 

 reverse names ; the kathode or negative pole is connected to the zinc or positive 

 metal ; the anode or positive pole is connected to the copper or negative metal. 

 The current enters the galvanometer by the anode, and leaves it on its way 

 back to the zinc by the kathode. Therefore, although the copper is electro- 

 negative, it may be spoken of as galvanometrically positive, and the zinc though 

 electro-positive, as galvanometrically negative. 



If we apply this to a muscle, we have seen that the current flows (in the wire 

 that connects the uninjured longitudinal surface to the cut end) from the longi- 

 tudinal surface to the cut end ; the longitudinal surface thus corresponds to the 

 copper of the Daniell cell, and is therefore electro-negative, though galvanometrically 

 positive ; similarly the cut end corresponds to the zinc, and is electro-positive though 

 galvanometrically negative. 



The omission of the qualifying prefix to positive and negative has led to a good 

 deal of confusion in physiological writings. A physicist uses the terms positive and 



