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Mr. .1. S. 



" The Demarcation Current of Mammalian Nerve. (Preliminary 

 Communication.) I. The Demarcation Current of Mammalian 

 Nerve." By J. S. MACDONALD, B.A., L.R.C.P.E., University 

 College, Liverpool, Research Scholar of the British Medical 

 Association. Communicated by Professor SHERRINHTOX, 

 F.R.S. Received July 28, 1900. 



1. A necessary preliminary to the study of the distribution of the 

 demarcation current and source is an examination of the character of 

 the resistance of the particular nerves in which phenomena are observed. 

 The resistance per cm. of the nerves examined vagus, phrenic, and 

 sciatic nerves of dog and cat, &c., varies with the nerve and with the 

 animal 



Vagus Horse, 2000 ohms per cm. 



Dog, 12,500 



Cat, 31,000 .. 



Sciatic Dog, 3500 .. 



Cat, 4500 .. 



the variations depending upon the character of the nerve and presum- 

 ably of the individual fibres, upon its sectional area, and probably 

 upon intrinsic differences between the average salt content of the 

 tissues of different animals. 



But taking any individual nerve the estimated value of the resistance 

 per cm. varies with the length of the piece, from the determination of 

 the resistance of which the estimation is made. 



Thus keeping one electrode at a fixed point of a nerve, the cross- 

 section A, moving a second electrode from point to point, B, C, D, &c., 

 and measuring the resistance included between A and these several 

 other points, a series of determinations of the resistance of various 

 lengths of the same nerve are made. From a knowledge of the length 

 of the piece and from this determination, an estimation of the resistance 

 per cm. of the nerve is obtained which is greater with each diminution of 

 length. 



Experiment. Vagus Nerve of Dog. 



