5 62 



COMPARATIVE ELECTRO-PHYSIOLOGY 



I give here a table which shows the galvanometric deflection 

 corresponding to each particular E.M.F. 



TABLE OF GALVANOMETRIC DEFLECTIONS AND CORRESPONDING E.M.F. 



In this particular experiment, it will be seen that the 

 an-electrotonic and kat-electrotonic effects are practically 

 equal. But, to be more accurate, the an-electrotonic are 

 slightly lower with low E.M.F., and slightly higher with 

 high, than the corresponding kat-electrotonic deflections. A 

 constant electrical current is thus seen to induce electro- 

 motive variations, outside its poles, in the vegetal nerve. 



We next turn to the question of the variation of 

 excitability induced in a tissue, by the passage of a con- 

 stant current. On this subject the most important con- 

 tributions have been made by Bernstein and Hermann. 

 Bernstein, experimenting on the sciatic nerve of frog, found 

 that excitation induced a polarisation decrement. This 

 experiment is illustrated in the following diagram (figs. 339, 



FIG. 339. FIG. 340. 



Figs. 339, 340. Diagrams illustrating Bernstein's Electrotonic Decrement 



Fig. 339 shows decrement of kat-electrotonic, and fig. 340 of an-electro- 

 tonic currents, under stimulation at s. In this and following figures 

 the inside thin arrow indicates direction of polarising current, the 

 outside thick arrow the direction of responsive current. 



340), In fig. 339 the kathodal effect is seen induced 

 in the extra-polar circuit. When the nerve is now excited 

 by tetanising electric shocks, a diminution of the extra-polar 

 current is induced. When the anodal effect is induced in 



