THE REACTION OF NORMAL AND ABNORMAL NERVE 143 



latter adjustment is used, the current must pass from the periphery 

 toward the center. It is then called an ascending current. 



In the second place, attention should be called to the fact that the 

 passage of a constant current through a nerve gives rise to certain 

 chemico-physical changes in the regions of the anode and cathode 

 which have been designated by DuBois-Reymond as electrotonus 

 (1843). This condition manifests itself in profound alterations in the 

 irritability and conductivity of the nerve. This change constitutes 

 physiological electrotombs, the one occurring in the region of the anode 

 being known as anelectrotonus and the one at the cathode as catelectro- 

 tonus. The physiological electrotonus finds its origin in the so-called 

 electrotonic currents which arise in consequence of electrolysis and 

 polarization. The latter may be designated as physical electrotonus. 



Nerve is a moist conductor and hence, it need not surprise us to 

 find that the passage of the galvanic current induces certain processes 

 of electrolysis and dissociation which attain their maximal intensity 

 at the electrodes, i.e., at the points of entrance and exit of the current. 

 Inasmuch as the acid negative ions of the electrolytes are transferred 

 to the anode, this region must assume an acid reaction, while the ac- 

 cumulation of the basic positive ions upon the cathode must render 

 the latter alkaline. In the course of time, this accumulation of nega- 

 tive ions upon the anode and of positive ions upon the cathode gives 

 rise to the so-called polarization current, i.e.; to an electrical inter- 

 change, the direction of which is opposite to that of the original polar- 

 izing current. 



This polarization becomes most intense if metal electrodes are 

 employed, but the aforesaid changes then appear to be confined to the 

 points of contact between the metal and the nerve. If non-polarizable 

 electrodes are used, this external form of polarization gives way to the 

 internal form. Although still most conspicuous at the anode and 

 cathode, these changes are then less closely restricted to the sur- 

 faces of the electrodes and spread with steadily decreasing density 

 into the region between these two poles as well as into those situated 

 immediately outside of them. The distance to which they extend out- 

 side the poles depends upon the strength of the primary galvanic cur- 

 rent. Thus, electrotonus may be said to be intrapolar and extrapolar^ 

 in its character. 



In this connection emphasis should be placed upon the fact that 

 these electrotonic currents are absolutely distinct from the nerve im- 

 pulse, as well as from the wave of negativity or action current and the 

 current of injury. Thus, it has been proven that their velocity is much 

 greater than that of the nerve impulse as betrayed by the speed of the 

 negative variation. ^ In the second place, it has been shown that they 

 may attain a strength twenty-five times greater than that of the cur- 

 rent of injury. Their distinctiveness is also indicated by the fact that 



^ Pfliiger, Unters. liber die Physiol, des Elektrotonus, Berlin, 1859. 

 ^ Gildermeister and Weis, Pfliiger's Archiv, xciv, 1903, 509. 



