342 ELECTEO-PHYSIOLOGY. 



the iuducted contraction was equally produced : tlie idea of the electric discharge 

 was not ou that account excluded, because it was proved by experiment that 

 under like conditions a slight discharge of the jar made itself felt upon the nerve 

 of the galvanoscopic frog. 



I propose to show still another experiment with the galvanoscopic frog which 

 will render clearer the nature of the inducted contraction. The inductive frog 

 being prepared and j^laced upon an isolating plane, I place two wicks of cotton 

 or strips of paper moistened with water in contact with the extremities of 

 the frog — that is, one of them in contact with the upper thigh and the other 

 with the leg — and I fold the two cushions in such a way as to leave an interval 

 of some millimetres free between their extremities. Having then some galva- 

 noscopic frogs, fresh and vivacious, the circuit is closed by placing their nerves 

 between the two wicks or strips. We shall now see the galvanoscopic frogs 

 contract each time that the entire frog undergoes contraction. If one of the 

 wicks be detached, if at any point this circuit is opened, the contractions of the 

 galvanoscopic frog are at an end. This result leads necessarily to the admission 

 that in the act of contraction a homogeneous conducting arc applied on the ex- 

 tremity of the muscle is traversed by an electric current, or rather by a discharge, 

 if we judge from its brief duration. 



By varying these experiments with the galvanoscopic frog, placing some with 

 the nerves in a certain direction, and others with the nerves in an opposite 

 direction, it will be found generally that the contraction does not take place 

 except in the galvanoscopic frogs whose nerves are extended from the inferior 

 to tl^ superior extremity of the inductive muscle. In a Avord, having two galva- 

 noscopic frogs, whose two nerves close the circuit, arranged one against the other, 

 the most constant inducted contraction takes place in that which has the leg 

 turned towards the upper extremity of the inductive muscle. Similar experi- 

 ments were tried upon animals of warm blood and with analogous results, 

 although such experiments are sufficiently difficult from the brief duration of the 

 muscular irritability in these animals. By supposing the moistened wicks, 

 placed in contact with the inductive thigh, to be progressively smaller, we may 

 pass from this case to that of the inducted contraction, and to the conclusion 

 that the phenomenon is of the same nature, as well in placing the nerve directly 

 on the muscle as in forming the arc in the manner I have shown. We thus 

 arrive at the conclusion that the inducted contraction is really the' effect of an 

 electric discharge Avhich occurs in the act of contraction, and the direction of 

 which, in the exterior arc, is contrary to the current of the same muscle in a 

 state of repose. . 



Inasmuch as the galvanoscopic frog is the most convenient instrument for the 

 study of electric currents of brief duration, it was proper to have recourse to 

 the galvanometer and to contemplate these electrical effects of contraction 

 through the accurate indications of that instrument. This was done by Dli Bois 

 Reymond in using a very delicate galvanometer and causing the inductive muscle 

 to contract several times in succession in order that the action might be prolonged. 

 The following is the mode in which he makes the experiment : A galvanoscopic 

 frog being placed on the cushions of the galvanometer, the nerve is kept isolated 

 in order to cause a series of electric currents to pass, which may in some measure 

 torpify the muscle, without giving room to the doubt that this current might 

 pass into the galvanometer. At first, as is natural, the needle deviates through 

 the muscular current. When the needle is distinctly fixed the muscle is made 

 to contract, and thereupon, if the contractions are strong and sustained, the 

 needle will be seen to move to zero, to pass beyond, and become fixed in the 

 opposite quadrant with a certain deviation, which lasts as long as the contractions 

 are strong. To remove every doubt of the exactness of the experiment, Du Bois 

 Reymond has satisfied himself that the same thing occurs from irritating the 

 nerve with heat or by mechanical means, or employing a frog poisoned with nux 



