306 ELECTRO -PHYSIOLOGY. 



These effects are transformed into the periods of Eitter and of Xobili, by 

 using, at the beginning, an intense current. We should then see from the first 

 the two members of the frog contract simultaneously as well at the closing as 

 the ojicning of the circuit. But in that case, whether it be that the nerves lose 

 excitability naturally or that this loss is hastened by the passage of the current 

 and the contractions excited, it results that, after twenty or thirty minutes, 

 more or less, according to the force of the current and the vitality of the ani- 

 mal, we have the phenomena of the so-called second period, which correspond 

 to those we obtained by using the fresh nerve and very weak current. When 

 the excitability of the nerve is diminished it is requisite that the current be 

 strong ; when the nerve is very excitable a feeble current is required. 



The exposition which has been given establishes as the first, most simple, 

 and most general of electro-physiological j)henomena the excitation of the nerve 

 at the commencement of the direct current. We also find it verified with the 

 dynamometer that a given direct current excites at the commencement of its 

 action the greatest muscular force. This simplicity, however, is no longer mani- 

 fested when we o])erate on nerves entire and united to the nervous centres. It 

 is easy to lay bare in a rabbit or a dog two long tracts of the sciatic nerves, 

 and to cause a direct current to pass through one of them and an inverse cur- 

 rent through the other. In this case it is a constant result that the greater con- 

 traction of the leg occurs at the closing of the circuit with the direct current, 

 and the same contraction scarcely ever fails at the opening of the circuit in the 

 member traversed by the inverse current. But the phenomena are not so dis- 

 tinct as in the frog, nor indeed as in the rabbit and dog when the nerves ai'e 

 divided at their exit from the spine. When this division is made, contraction 

 occurs at first with the inverse current at the closing of the circuit, and it is 

 necessary to prolong the passage of this current through the nerve if Ave would 

 cause the anomaly to disappear and the contraction again to occur at the cessa- 

 tion of the inverse current. 



By operating upon dogs and rabbits we have the great advantage of being 

 able also to follow up the sensational effects which the current produces in the 

 animal. The most constant phenomenon which is remarked in these cases, and 

 which Bellingeri and Marianini have also verified in the living frog, is that the 

 symptoms of pain arise when the direct current ceases and the inverse com- 

 mences ; that is, when the contractions terminate. At these two instants we 

 realize likewise contractions in the back of the animal, occasioned by the so- 

 called reflex action, as is proved, in effect, by dividing the spine at different 

 points, when those contractions become successively circumscribed between the 

 nerve irritated by the cmrent and the point at which the spine is divided. 



To these phenomena pertains an old experiment of 5larianini, Avhich has 

 been of late extensively studied and varied by an eminent French physiologist, 

 Dr. Chauveau, of Lyons. Marianini employed a voltaic pile of 50, or GO, or 

 100 elements; Chauveau uses apparatus of induction — that is, inductive currents. 

 The former closed the circuit of the battery with his two hands, after having 

 jnoistened them. This, it will be readily seen, is the experiment which we 

 have witnessed with the divided frog, one nerve of which is traversed by the 

 direct and the other by the inverse current. In the experiment of Marianini 

 in like manner there is an arm traversed by the direct current, being the one 

 which touches the negative pole, and in which the contractions are excited by 

 the electric streams m liich traA'erse the muscular mass, as well as those which 

 traverse the nerves in the direction of their ramification. In this arm, there- 

 fore, exist the conditions for rendering the shock and the contractions greater 

 than in the other arm. 



In the experinients of Dr. Chauveau tlie two electrodes are applied at two 

 points, more or less widely separated, of the same muscular mass or of two 

 different muscles. He found that the greater contraction is always in the proxi- 



