THE EEACTION OF NORMAL AND ABNORMAL NERVE 147 



this connection reference should also be made to the work of Bethe^ 

 who has shown that the anodic and cathodic regions possess different 

 staining qualities. At the anode, the neurofibrils of the axis-cylinder 

 lose their power of absorbing methylene-blue, while those situated at 

 the cathode, show an abnormally high affinity for this dye. 



The relative amplitudes of the contractions obtained by stimu- 

 lating different points of the anodic and cathodic areas, have been 

 made use of in the construction of a curve illustrating the manner 

 in which the excitability of nerve is changed during the passage of 

 the galvanic current. The following schema of Pfltiger^ (Fig. 87) 

 shows that the subthreshold anode and suprathreshold cathode lines 



Fig. 87. — Electbotonic Alterations of Irbitability Caused by Weak, Medittm, 

 AND Strong Battery Currents. 

 A and B indicate the points of application of the electrodes to the nerve, A being 

 the anode, B the cathode. The horizontal line represents the nerve at normal irrita- 

 bility; the curved lines illustrate how the irritability is altered at different parts of the 

 nerve with currents of different strengths. Curve 2/^ shows the effect of a weak current, 

 the part below the line indicating decreased, and that above the line increased irrita- 

 bility, at x^ the curve crosses the line, this being the indifferent point at which the 

 catelectrotonic effects are compensated for by anelectrotonic effects; y"^ gives the effect 

 of a stronger current, and ^^ of a still stronger current. As the strength of the current 

 is increased the effect becomes greater and extends farther into the extrapolar regions. 

 In the intrapolar region the indifferent point is seen to advance with increasing strengths 

 of current from the anode toward the cathode. {American Text-hook of Physiology.) 



must vary in their position with the irritability of the nerve experi- 

 mented upon and the strength of the constant (polarizing) current. 

 This implies first of all that the polarization, or rather, the effect of 

 the polarizing current must increase with the irritability of the nerve, 

 and secondly, that the length of nerve so affected must increase with 

 the strength of the current. At the point of confluency of these anodic 

 and cathodic fields in the intrapolar region, a conflict arises in conse- 

 quence of which the irritability remains unchanged. With a weak 

 polarizing current, this indifferent point lies near the anode, while with 

 stronger currents it is shifted more and more toward the cathode. 

 This fact implies that strong currents are more depressant than weak 

 currents, and hence, a point will eventually be reached when the 

 depression also involves the cathode. The making increase in excita- 



^ AUg. Anat. und Physiol, des Nervensystemes, Leipzig, 1903. 

 ' Unters. iiber die Physiol, des Elektrotonus, Berlin, 1859. 



