ELECTRO-PHYSIOLOGY. 305 



nerve, beyond the poles, another poi'tion of current, called derivative, opposite 

 in direction, and which may have a greater effect than the first. To represent 

 this case, let us suppose we have a piece of string or pack-thread slightly wet 

 and bent like the letter Q inverted, the extremities of which touch a surface 

 forming a good conductor, such as a metallic plate. If we now apply two poles 

 of the battery to the string, we know that the electricity will divide into two 

 parts — that is, into one portion which traverses the string between the two poles, 

 and into another portion which circulates beyond them, and which, meeting in 

 the plate with a much better conductor than the string, may be even greater 

 than the first. What it most imports for us to notice is, that if the current in 

 the intermediate part of the nerve between the two poles be, for instance, direct, 

 in the lateral parts of the same nerve it will be inverse, llence the confusion 

 which may arise in making an experiment under these conditions in order to 

 judge of the effects due to the direction of the current. 



Let -US recur to the frog divided in half, and cause the discharge from the jar 

 to pass from one member to the other, or from one nerve to another, while the 

 animal is stretched on the metallic arms of the universal discharger. I have 

 recourse to the small Leyden jar, and which, after being charged by a few 

 turns of the machine, I discharge two or three times with a metallic arc. Thus 

 reduced, so as no longer to yield signs of electricity with an electroscope, the 

 discharge is turned upon the extended frog, when that member alone which 

 communicates with the external armature, and the nerve of which, therefore, is 

 traversed by the direct discharge, will be observed to contract two or three 

 times in succession. In using the discharge of the jar we can only take ac- 

 count of the first effect, although in reality this must be composed of two oppo- 

 site phases, which immediately succeed one another. With induction, also — that 

 is, on generating an inductive current, as with the physiological effect, the dis- 

 charge of the jar acts in that phase only which corresponds to the closing of 

 the circuit in the case of the battery. 



Let us substitute the battery for the jar, employing, however, the weakest 

 possible current. With this view I take a glass tube, having an internal diam- 

 eter of three or four millimetres, and a length of one metre ; this tube is bent 

 to the form of an U, and is fixed upon a wooden table. Having filled it with 

 distilled water and plunged the metallic rheophores of the battery more or less 

 into the liquid column, we obtain in the circuit a strong resistance, varying ac- 

 cording to the length of the column. The frog having been prepared iu the 

 usual manner, and extended on the two wires of the discharger, so that the 

 current shall traverse it from one member to the other, it follows that the cur- 

 rent in one of the nerves will be direct, in the other inverse. I begin by using 

 as long a column of water as possible, so that, whether from the greatly dimin- 

 ished intensity or the slowness wath which the permanent electric state is estab- 

 lished, neither of the members of the frog is contracted, either at the opening 

 or closing of the circuit. I gradually diminish the height of the column of wa- 

 ter, and the first contraction which ensues is always that of the member whose 

 nerve is traversed by the direct current in the act of closing the circuit. I con^- 

 tinue to diminish the liquid column, or, in other words, to increase the intensity 

 of the current, and a second contraction supervenes, that, namely, of the niem- 

 ber traversed by the inverse current at the opening of the circuit. If the cur- 

 rent be still augmented, both contractions show themselves as if at the same 

 instant ; that is, in the member traversed by the inverse current at the closing, 

 and in the other traversed by the direct current at the opening of the circuit. 

 By proceeding with our experiments on the same frog I might show that if the 

 current be now again reduced we shall repass through an inverse succession of 

 the same phenomena, and in the end obtain, with the weakest current, only a 

 contraction iu the member traversed by the direct current and at the closing of 

 the circuit. 



20 s. 



