102 THE SIGNS OF LIFE [I.ECT. 



galvanometer you see an effect (or after-effect) in that same 

 direction. I turn over the reverser of the exciting current, I 

 apply a similar induction shock in the outgoing direction ; the 

 response (or after-affect) as you see, is again to your left, in the 

 ingoing direction, and it is larger than the previous one ; there 

 is perhaps a polarisation factor (ingoing after outgoing) that 

 makes this ingoing response larger than in the previous case, 

 where the polarisation factor (outgoing after ingoing) was 

 opposite to the main physiological ingoing effect but that is a 

 detail. The principal point is, that the effects of electrical 

 excitation of whatever direction have been ingoing, or as I 

 choose to call it " negative." 



The effects of excitation in either direction being ingoing, it 

 is clear that a series of currents of alternating directions will 

 produce an ingoing effect. Tetanisation, i.e., a series of make- 

 and-break current in rapid succession, will therefore produce an 

 ingoing effect ; and as you now see, that ingoing effect is off 

 scale to your left ; there has been a summation of separate 

 stimuli forming the tetanising series. 



I reverse the direction of the tetanising currents, and as 

 before, you see the spot flying off scale to your left, indicating 

 response (or more precisely after-effect) through the directly 

 excited pad in the ingoing direction. 



This has been a single experiment. I do not remember 

 having ever seen better marked ingoing effects of excitation ; 

 but the pad was very fresh, and I did not use very strong 

 tetanisation, which two conditions have been shown by previous 

 experiments to be favourable as regards the demonstration of 

 ingoing effects of direct excitation. In previous experiments I 

 have indeed observed precisely the reverse effects, viz., outgoing 

 effects by direct excitation ; but I was then following out the 

 effects day by day, and using excitation of full strength, in 

 order to learn how long after the death of a cat this sign of life 

 was observable on one of its feet. 



Such a pad has now been set up, taken from a cat twenty- 

 four hours after death, and you see as a matter of fact that it 

 gives large outgoing effects (deflections to your right) after both 

 directions of strong tetanisation, 



