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HANDBOOK OF PHYSIOLOGY, 



crease in irritability is called katelectrotonus, and similarly the 

 decrease is called anelectrotonus. As there is between the electrodes 

 both an increase and a decrease of irritability on the passage of a po- 

 larizing current, it must be evident that the increase must shade off into 

 the decrease, and that there must be a neutral point where there is 

 neither increase nor decrease of irritability. The position of this 

 neutral point is found to vary with the intensity of the polarizing cur- 

 rent when the current is weak the point is nearer the anode, when 



Fig. 339. Diagram illustrating the effects of various intensities of the polarizing currents. 

 n, n', nerve ; a, anode : k. kathode ; the curves above indicate increase, and those below decrease 

 of irritability, and when the current is small the increase and decrease are both small, with the 

 neutral point near a, and so on as the current is increased in strength. 



strong nearer the kathode (fig. 339) ; when a constant current passes 

 into a nerve, therefore, if a contraction result, it may be assumed that 

 it is due to the increased irritability produced in the neighborhood of 

 the kathode, but the breaking contraction must be produced by a rise 

 in irritability from a lowered state to the normal in the neighborhood 

 of the anode. The contractions produced in the muscle of a nerve- 

 muscle preparation by a constant current have been arranged in a table 

 which is known as Pfluger's Law of Contractions. It is really only a 

 statement as to when a contraction may be expected : 



The difficulty in this table is chiefly in the effect of a weak ascending 

 current, but the following statement may remove it. The increase of 

 irritability at the kathode when the current is made is more potent to 

 produce a contraction than the rise of irritability at the anode when the 

 current is broken; and so with weak currents the only effect is a con- 

 traction at the make of both currents. The descending current is more 



