118 NEKVOUS SYSTEM. 



zinc. The experiments were then arranged so as to operate 

 first with the platinum wire and afterward with the zinc, by 

 passing a galvanic current through a small portion of the 

 conductor, in the same way as it is passed through a portion 

 of a nerve. He found that in this way he could produce a 

 strong electrotonic current in the platinum wire, even at a 

 distance of more than three feet from the electrodes, while 

 no such current was observed in the zinc. He remarks that 

 in the platinum wire " secondary polarities " are produced 

 very powerfully and rapidly, while these are not developed in 

 the zinc. 1 From these experiments alone, it might seem that 

 the phenomena of electrotonus, as described by Du Bois-Rey- 

 mond and others, are to be explained entirely by the physi- 

 cal properties of the nerves as conductors of electricity ; but 

 various observations on the nerves tinder different condi- 

 tions have conclusively proven the contrary. All observers 

 are agreed that the electrotonic condition is marked in pro- 

 portion to the excitability of the nerve, and is either entirely 

 absent or extremely feeble in nerves that are dead, or have 

 lost their irritability. If a strong ligature be applied to the 

 extra-polar portion of the nerve, or if the nerve be divided 

 and the cut ends brought in contact with each other, the 

 electrotonic condition is either not observed or is very feeble. 

 These facts show conclusively that the phenomena of elec- 

 trotonus depend upon the physiological integrity of nerves. 

 A dead nerve, or one that has been divided or strongly liga- 

 tured, may present these phenomena under the stimulation 

 of a very powerful current (and then only to a slight degree), 

 when the condition depends upon the purely physical prop- 

 erties of the nerve as a conductor ; but there is no compari- 

 son between these phenomena and those observed in nerves 

 that retain their physiological properties. Were it other- 

 wise, how could the physiological properties of a diseased 

 nerve be restored throughout its whole extent by a constant 

 current passed through a restricted portion, when the exci- 



1 Revue dcs court scientifiques, Paris, 1867-'68, tome v., p. 279. 



