ELIiCTRO-FIIYSIOLOGY. 311 



I should also point out a mode of producing tlie contractions by the opening 

 of the circuit, which, however simple, might, in minds not habituated to reason- 

 ing upon these experiments, give occasion to erroneous interpretations. I take 

 a frog prepared as usual, and, after passing the current for some time, touch with 

 a small pencil, wet with water or some other liquid, the nerve traversed by the 

 direct current — no result ensues ; I touch the other nerve with the wet pencil, 

 and instantly violent con^-actions tijke place in this member. When this ex- 

 periment is seen for the first time, it is not easy to hit upon the cause of the 

 phenomenon, though very simple, and one might almost be induced to surmise 

 a specific action of the liquid on the two nerves. But with a little reflection it 

 is readily understood that when the nerve traversed by the inverse current is 

 wet with a drop of v/atcr, this drop, which envelopes the nerve, has upon that 

 nerve the effect of an opening of the circuit ; the current leaves the nerve to 

 enter into the liquid, which conducts it much better, and we have the contraction 

 at the opening of the circuit in the member traversed by the inverse current. 



These considerations being premised, it is time to see what takes place in the 

 case of the prepared frog submitted from fifteen to twenty minutes or more to 

 the passage of a current. At the moment I open the circuit the member 

 traversed by the inverse current, and that alone, undergoes contraction, and for 

 the most part remains tetanized or rigid for several seconds. If I then close 

 the circuit there is no contraction cither in the inverse merhber or in that per- 

 meated by the direct current ; or if there be any in the latter it is slight, and 

 ceases after the same experiment has been repeated three or four times. If the 

 circuit be reclosed immediately after having been opened, that is during the time 

 when the inverse member is still tetanized, we shall see this member relax and 

 contraction cease. This experiment is equally verified if the current be made 

 to pass directly from nerve to nerve without traversing the muscles; only in this 

 case the described effect is produced in less time than when the current traverses 

 the entire animal. The same results are witnessed when we operate on the living 

 frog or the higher animals; but here the effect is produced more slowly, and it is 

 with difficulty that we realize in the living animal that prolonged tetanic con- 

 traction displayed in the inverse member of the prepared frog on opening the 

 circuit. 



These results conduct us to the following proposition : "A continuous current 

 transmitted in a mixed nerve modifies the excitability of the nerve in a different 

 and it may even be said an opposite manner, according to its direction; the direct 

 current enfeebles and destroys the excitability of the nerve, while the inverse 

 increases it within certain limits. The time necessary for the current to produce 

 these effects is proportional to the degree of excitability of the nerve and in in- 

 verse ratio to the intensity of the current. After the opening of the circuit the 

 effects of the current have a tendency to disappear, and so much the more rapidly 

 as the excitability of the nerve is greater and the current employed was weaker." 



It is important to show that independently of the use of the electric current, 

 the two nerves which have been traversed hy that current have acquired a dif- 

 ference of excitability — that is to say, that in the nerve traversed by the direct 

 current the excitability is much diminished or even extinguished, while on the 

 other hand it is preserved or increased in the nerve traversed by the inverse 

 current. For this purpose I take away one of the prepared frogs which has 

 been subjected to the passage of the current, and touch first one and then the 

 other of its nerves with a piece of potassa or hot iron, or wound them with the 

 forfex. Whichsoever of these means is employed to excite the nerve, you will 

 see contraction take place if I operate on the nerve which transmitted the in- 

 verse current, while none occurs from similar action on the nerve traversed by 

 the direct current. 



The above proposition brings to view and at the same time explains the phe- 

 nomenon discovered by Volta, which is still called in electro-physiology the 



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