Dr. RadclifFe on the Action of a Galvanic Current upon Nerve. 391 



among other things of the muscular movements resulting from the 

 action of a galvanic current upon a motor or mixed nerve, Pro- 

 fessor Claude Bernard says that some of the more important of 

 these movements have been overlooked, and he quotes an account 

 of some investigations by Dr. Rousseau of Vezy, which do away with 

 certain very perplexing variations in the order of these movements. 



The movements resulting from the action of a galvanic current upon 

 nerve are usually divided into the three periods of double, alternate, 

 and single contraction which are set down in the following Table : — 



Professor Bernard proposes to place another period before the 

 first of these — a period corresponding to the normal unexhausted 

 and undisturbed state of nerve, and characterized by contraction at 

 the beginning of the two currents, direct as well as inverse. 



The investigations of Dr. Rousseau show how it is that the order 

 of these contractions is altered by certain Changes in the arrange- 

 ment of the nerve acted upon by the current. If the nerve acted 

 upon be divided and lifted up at its end, so as to break the circuit of 

 the derived current*, the order of contraction is that which is put 

 down in the preceding Table ; if the nerve acted upon be raised in a 

 loop (either without dividing it, or, after dividing it, by dropping down 

 the end); so as not to break the circuit of the derived current, the 

 order of contraction is that which is represented in the following 

 Table :— 



* Figures 3 & 4 on page 396 may serve to illustrate all that need be said 

 respecting the derived current. In figure 3, the sciatic nerve of a frog's leg is 

 arranged in a loop across the poles P N of a galvanic apparatus ; the primitive 

 current, indicated by the black arrow, passes by the shortest route from the 

 positive pole P to the negative pole N ; the derived current, indicated by the dotted 

 arrows, passes by the longest route between these poles, and as it also proceeds 

 from the positive pole P to the negative pole N, it passes in the contrary direc- 

 tion to that of the primitive current. In fig. 4, the sciatic nerve is divided 

 between P and the thigh, as is meant where the nerve is spoken of as divided 

 and lifted up at its end ; and being divided, the only current passing is the primi- 

 tive current ; for the circuit of the derived current being broken, there can be no 

 derived current in this case. 



