CHAPTER IV. 



THE ELECTRICAL PHENOMENA SHOWN BY NERVE 

 AND MUSCLE, 



The Demarcation Current. Our definite knowledge of the 

 electrical properties of living tissue began with the celebrated in- 

 vestigations of du Bois-Reymond* (1843). When a muscle or 

 nerve is removed from the body, and, in the case of the muscle, 

 when one tendinous end is cut off, it is found that the cut end has 

 an electrical potential differing from that of the uninjured longi- 

 tudinal surface of the preparation. Following the usual nomen- 

 clature, the cut end is electronegative, the longitudinal surface 

 is electropositive. If, therefore, the longitudinal surface is con- 

 nected by a conductor with the cut surface a current will flow from 

 the former to the latter, as is indicated in the accompanying dia- 

 gram. 



Fig. 37. Schema showing the course of the demarcation current in an excised nerve, 

 when a point on the longitudinal and one on the cut surface are united by a conductor. 



While the direction of the current through the conductor con- 

 necting the two points is from the longitudinal to the cut surface 

 the current may be considered as being completed in the opposite 

 direction within the substance of the muscle or nerve, as shown 

 in the diagram. We may, in fact, consider an excised nerve or 

 muscle as a battery, the cut end representing the zinc plate and 

 the longitudinal surface the copper plate. Within the battery 

 the direction of the current is from zinc to copper, from cut end 

 to longitudinal surface; outside the battery the direction is from 

 copper to zinc, from longitudinal to cut surface. If two wires 

 are connected with the muscle or nerve the end of the one attached 

 to the longitudinal surface will represent the positive pole or anode, 

 the end of the one attached to the cut end will represent the cathode 



* "Untersuchungen iiber thierische Elektricitat," du Bois-Reymond, 

 1848-1860. 



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