588 FUNCTIONS OF THE CEREBRO-SPINAL NERVOUS SYSTEM. 



constitutes Pfliiger's extrapolar centripetal cathelcctrotonus. By a similar 

 mode of proceeding, the excitability of the nerve behind the ascending cur- 

 rent, or in the inyopolar portion, which is under the influence of the positive 



FIG. 199. 



N 



^^ 



N N, represents a nerve ; M, a muscle ; c c, the positive and negative poles of a constant current, a /, 

 extrapolar portion of nerve, d, point to which a stimulus, here represented by R R, the positive and 

 negative poles of an interrupted current, but which may be replaced by a mechanical or chemical ex- 

 citant, is applied. 6, c, indicates the line of normal excitability, supposed for the sake of simplicity to 

 be equal throughout the whole length of the nerve, though in reality it is greater, and should therefore 

 ascend towards b. b, e, y, indicates the curve of augmented excitability in the extrapolar portion of 

 nerve, the amount of increase being greatest at the cathode as at g, less marked at e, and falling to its 

 ordinary amount at b. 



pole of the constant current, c c, can, as by the curve /, e, c, in Fig. 200, be 

 shown to be remarkably diminished. This constitutes Pfliiger's extrapolar 



Fro. 200. 



-o 



Centrifugal Extrapolar Anelectrotonus. The references are the same as in the last figure except that 

 af represents the intrapolar portion of the nerve, and that the curve of diminished excitability is 

 represented by /, e, c; the lowest degree being at the anode, /, and the nerve gradually recovering its 

 normal excitability towards c. 



centrifugal anelectrotonus. The curve, g, e, c, in Fig. 201, shows the varia- 

 tion in the excitability in the myopolar portion of the uerve, when the Nega- 



FlG. 201. 



Extrapolar Centrifugal Cathelectrotomis. The increase in the excitability of the nerve is shown by 

 the curve, g, e, c, to be greatest in the vicinity of the cathode of the polarizing current, c, c. 



