670 . PHYSIOLOGY. 



tion becoming greater than the kathodic closure contraction. In 

 neuralgias the anode is placed upon the painful nerve. 



The Faradic current is a more effective stimulus to nerves than 

 a galvanic current, for the effectiveness of a current as a stimulus 

 depends not only upon the total variations in intensity, but also 

 upon the amount of such variation in the unit of time; that is, the 

 greater the rapidity of the total variation, the more effective is the 

 current as a stimulus. 



In the Faradic current the kathode is always more active in pro- 

 ducing contractions. The short duration of the opening and closing 

 of the induction currents makes them fused in effects. 



ELECTROTONIC VARIATION OF ELECTROMOTIVITY. Electrotonus 

 not only changes the irritability and conductivity, but also the elec- 



Anelcctrotonic Polarising JEatelectrotonic 

 current current current. 



Fig. 270. (WALLER.) 



tromotivity of a nerve. If a nerve is connected with nonpolarizable 

 electrodes in such a way that its transverse section is laid on one and 

 its surface on the other, then the galvanometer will show the pres- 

 ence of a strong nerve-current. If, now, a galvanic current is passed 

 through the extremity of the nerve outside the unpolarizable elec- 

 trodes, the polarizing current is established. The electrotonic cur- 

 rent in the nerve always has the same direction as the polarizing 

 current. 



In the extrapolar kathodic region an electrotonic current is gen- 

 erated when the polarizing current is closed. In the anodic region 

 the electrotonic current is stronger than the kathodic current. 



These electrotonic currents are only found in medullated nerves, 

 and are only produced by an electrical polarizing current. Non- 

 medullated nerves, muscles, and tendons do not show them. The 

 electrotonic currents are not the action-currents of a nerve, and 

 must not be confounded with them. 



The experiment of paradoxical contraction depends upon elec- 

 trotonic currents. 





