IV.] 



DIRECT EFFECTS 



67 



0. 10 volt. The positive response is declining, rapidly at first, 

 then more slowly, and as soon as the spot is fairly steady, I 

 compensate and repeat the excitation in the reverse (ingoing) 

 direction, and, as before, you witness a large positive (outgoing) 



voit 



oa 



30 mms. 



FlG. 30. Frog's skin. Response to direct electrical excitation. The first 

 deflection is by a standard voltage. The next two small deflections are in response 

 to + and - break induced shocks with the coil at 1000 units. The last two large 

 deflections are with the coil at 5000. (The principal "outgoing" effect is preceded 

 by a brief ingoing effect in the case of ingoing excitation.) 



deflection, which, although in the direction of a polarisation 

 counter-current, is a blaze-current, like the antidrome blaze- 

 current of the eyeball (p. 47). Indeed, these skin effects are 

 precisely similar to the effects you have already seen in the 

 case of the eyeball. The positive response to positive excita- 

 tion is the unequivocal blaze, the positive response to negative 

 excitation is the equivocal blaze. 



And to complete the proof, I will kill the skin either with 

 a few drops of mercuric chloride solution, or by plunging it 

 into hot water, and now the skin gives no response at all 

 to either direction of excitation. The spot does not stir. If I 

 unshunted the galvanometer we might see the small polarisa- 

 tion effects that occur with any electrolyte. But this is an 

 unessential point, and we will leave the galvanometer as it is 



