iv.] ABC 69 



shock at the same strength of coil. This is a summation of 

 effects. Moreover, if a strength of coil be taken so small as 

 to produce no response with single shocks, tetanisation at the 

 same strength will bring out an evident or even large positive 

 response. Notice that, in making this experiment with tetanisa- 

 tion, I have taken the response immediately after and not 

 during tetanisation. A similar effect can be brought out during 

 tetanisation, and 'in cases (like the present) where there is a 

 clear and manifest effect in one direction, we may without 

 fear of fallacy demonstrate that effect during as well as after 

 tetanisation. But in doubtful cases (p. 131) there is con- 

 siderable difficulty in distinguishing a true blaze-current from 

 the disturbance of the galvanometer by the necessarily strong 

 currents i^sed, and from the relatively large polarisation currents 

 manifested during strong tetanisation. For this reason I have 

 deliberately abstained from laying any stress upon the effects 

 produced during tetanisation, and have limited myself to the 

 information obtainable with and after single shocks, and after 

 tetanisation. 



| 43. The ABC plan. With a piece of skin arranged as 

 shown in Fig. 32, an induction current passed through the 

 skin in the positive direc- 

 tion from B to A has its 

 anode at the lower surface 

 B and its kathode at the 

 upper surface A. A blaze- 

 current is aroused in that 

 same direction from B to 

 A, and we put to ourselves 

 the question whether that 



current depends upon an electro-positive state at B, or upon an 

 electro-negative state at A, or upon both states. Or more 

 familiarly put : is the B to A current by push of B, or by pull 

 of A, or by both? 



The question will be answered by the following plan of 

 experiment, which will enable us to examine separately the two 

 surfaces B and A by connecting first one, then the other, with an 



