ACTIOX OF ELECTRICITY UPOX THE NERVES. 100 



In the usual way for such experiments, be subjected to a feeble 

 galvanic current, there is a time when muscular contraction 

 takes place only at the instant when the circuit is made ; no 

 contraction occurring when the circuit is Broken ; and this 

 occurs only with the direct current ; i. e., when the current 

 flows toward the periphery, the positive pole being above, 

 and the negative below. If the poles be reversed, so that 

 the galvanic current flows from the periphery toward the 

 centres the inverse current contraction of the muscles 

 occurs only when the circuit is broken and none takes place 

 when the circuit is closed. 



These phenomena are distinct after the irritability of the 

 parts has become somewhat diminished by exposure or by 

 electric stimulation of the nerve, but they may occur in per- 

 fectly fresh parts, when the galvanic current is very feeble. 

 Usually, when the nervous irritability is at its height, con- 

 tractions occur both on closing and breaking the circuit ; but 

 they are more powerful on closing the circuit, for the direct 

 current, and on breaking the circuit, for the inverse current. 

 This fact has been noted by all experimenters since the time 

 of Hitter, by whom the essential characters of these phenom- 

 ena were first described. 1 Hitter was in error in supposing 

 an antagonistic action of the flexor and extensor muscles 

 excited by making the circuit with the direct, and breaking 

 the circuit with the inverse current ; but most of his descrip- 

 tions of the effects of different currents are remarkably 

 accurate and have been fully confirmed by late observers. 



A very simple experiment made by Matteucci strikingly 

 illustrates the contrasted action of the direct and the inverse 

 current. The posterior extremities of a frog are prepared 

 so as to leave the nerves on the two sides connected together 

 by a portion of the spinal column. The legs are then placed 

 each one in a wineglass of water, and a feeble galvanic cur- 

 rent is passed from one glass to the other. It is evident 



1 RITTER, Beytrage zurndhern Kenntniss des Gralvanismiis, Jena, 1805, Bd. ii., 

 drittes, viertes und letztes Stuck, S. 132, et seq. 



