ELECTRO-PHYSIOLOGY. 343 



vomica. From all which he coacliules: "that iu the act of contraction the 

 electro-motor power of a muscle is diminished, whence the opposite current due to 

 the secondary polarity of the laminae being enabled to prevail over the muscular 

 cun-ent, not only does the needle descend to zero, but it is compelled to deviate 

 in an opposite direction." When the experiment is made by using two opposed 

 gastrocuemians, one of .which alone is made to contract, the explanation is still 

 more easy, according to Du Bois lleymond, for then it is the current of the 

 muscle left in repose which is the prevalent one, and which compels the needle 

 to deviate in the contrary direction. 



As to the phenomenon of the inducted contraction, properly so called, Du Bois 

 Raymond admits that when the nerve of the galvanoscopic frog is placed in con- 

 tact with the muscle the muscular current circulates in it, and that the rapid 

 diminution or negative variation, as he calls it, of the same current, is the cause 

 of the contraction of the galvanoscopic frog. This supposes that in the nerve of 

 this frog the circuit of the muscular current is constantly established : instead of 

 which we have seen that the inducted contraction is obtained, whatever be the 

 manner in which the nerve is disposed ; that it occurs from only touching with 

 the nerve the extremities of the leg of the frog, and that, following at the moment 

 of the contraction, it results that the nerve is traversed by a discharge which is 

 in ai^ opposite direction to the muscular current. 



It occurred to me that to remove every doubt on the interpretation of the 

 electric phenomenon which accompanies the contraction, it would be sufficient to 

 repeat the experiments with the galvanometer by the method which excludes 

 the secondary polarity. This I have done after having satisfied myself that 

 there was in fact no sensible trace of secondary polarity, even after having 

 caused to pass in the laminae currents much more intense than the muscular 

 current. Xow, even in this manner, when strong contractions are excited in the 

 muscle placed in the circuit of the galvanometer, the needle immediately declines 

 and continues to oscillate for some moments iu the opposite quadrant. In a 

 word, the result is not different when the secondary polarity of the laminse eaters 

 into the experiment or when this polarity is entirely excluded. To succeed 

 better with the experiment, instead of the gastrocuemian, the thigh of the frog 

 may be used, by which we have from the first a muscular current which is small 

 and often even null. Then, under the contractions the deviation of the needle 

 immediately takes place in the same direction in which that deviation occurred 

 when the muscular current circulated from the first in the galvanometer. 



I propose also a simple arrangement Avith which the experiment succeeds 

 more easily and certainly. In a piece of varnished wood I form two cavities in 

 the shape of the two connected thighs of a frog. In the same wood is formed 

 another cavity divided into two compartments which are filled with sulphate of 

 zin^, and in which are immersed the amalgamated laminse of the galvanometer. 

 I take a lively frog and reduce it to the two thighs alone, leaving the lumbar 

 nerve to a single thigh. The other thigh, though not. meant to contract, is left 

 only that there may not be a transverse incision in the inductive thigh, which 

 would introduce a new cause of the muscular current. To establish the circuit 

 I use two pieces of hempen string secured with sealing-wax to a plate of glass, 

 which is so placed that on one part the two strings touch the extremities of the 

 galvanometer, and on the other two points of the thigh at a distance of about 

 ten millimetres apart. The thigh should be pressed with the lamina, that it 

 may be certain that during the contraction the contact remains unaltered. Gen- 

 erally, when the circuit is closed, there is a slight deviation, first in one direction, 

 then in the other, as is known to occur from touching in various points the 

 muscle of the thigh. We now irritate the lumbar nerve with a current several 

 times in succession, which nerve is kept suspended and isolated by a silk thread. 

 The deviation which results, and which continues as long as the strong con- 

 tractions of the thigh endure, always indicates a current Avhich is directed in 



