70 THE SIGNS OF LIFE [LECT. 



indifferent point C through the galvanometer. And having 

 done this by a first pair of trials with excitation from B to A, 

 we shall complete the experiment by a second pair of trials 

 with excitation in the opposite direction from A to B, i.e., A 

 having been anodic, and B having been kathodic, and the 

 blaze-current being as before in the outgoing direction from 

 B to A. 



Try to forecast the result a priori, as I did ; I think you will 

 probably guess wrong, as I did. I imagined at this stage that 

 we had to do with something of the nature of so-called positive 

 polarisation, which Hermann and Hering have shown to be in 

 reality (in the cases of nerve and muscle) post-anodic action 

 current. On this view, the positive effect in the first case was 

 presumably due to a post-anodic "push" at B, and we should 

 therefore expect current through the galvanometer from C to B 

 (in the skin from B to C). But the positive effect in the second 

 case could not be explained, post-anodic " push " should be in 

 the negative direction, and the effect observed was evidently 

 either by post-anodic "pull" or by post-kathodic "push" 

 (through the skin). 



So I gave up forecasting and proceeded to experiments, of 

 which I hope you now see the interest. 



We shall begin by a first pair of trials to localise the seat of 

 electro-motive change in the case of the unequivocal blaze- 

 current, positive response to positive shock. We shall examine 

 the anodic surface B. Therefore, we have to compensate B with 

 C (the indifferent point) through the galvanometer, then to send 

 an induction shock through B A, then to reconnect B C with the 

 galvanometer to observe the altered electrical state of B. All 

 which we have now done, and find somewhat to our surprise that 

 the spot does not stir, i.e., that the electrical state at B has not 

 been altered. You suspect, perhaps, as I did, that there is a 

 break in the galvanometer circuit, so I throw a ^oV^y v lt mto 

 circuit, and you see by the movement of the spot that the circuit 

 is all right. 



We next examine the kathodic surface A, so I balance A 

 with C (the indifferent point) through the galvanometer, send 

 then an induction shock through B A, and finally reconnect A C 



