REVERSED POLAR EFFECTS IN LIVING TISSUES 209 



at anode. The action of anode-break was here much 

 stronger than that of kathode-make. 



(3) At make— Fall of kathodic leaf; no action at anode. 

 At break — No action at kathode ; response at anode. 



(4) At make — Kathodic action became feeble, and anode- 

 fall, though at make, the more pronounced of the two. 



At break — No action at either electrode. 



(5) At make. — No action at kathode; feeble action at 

 anode. 



At break — No action at either electrode. 



In tracing out the changes which are here taking place at 

 each electrode, we are struck by their progressive character. 

 If we fix our attention first on the kathode, we find that the 

 normal effect in the first of the series is gradually diminished, 

 till it disappears in the last. Again taking the anode, we 

 find a still more remarkable change, of a periodic character. 

 In the first experiment, we observe the most pronounced 

 abnormality, or reversal of the series, inasmuch as there was 

 response at make and none at break. In the second, the 

 response is tending towards normal, the anode-make effect 

 being feeble, and the break strong. In the third, the anodic 

 response has become normal, for there is no action at make, 

 but excitation at break. In the fourth, we again see a ten- 

 dency towards reversal, inasmuch as again there is response 

 at make and none at break. The same state of things, 

 though in a less degree, occurs in the fifth experiment. 



We have thus observed two different conditions, each of 

 which may contribute to produce this reversal of polar effects. 

 These are, firstly, the influence of a high E.M.F., which, at or 

 beyond a certain critical value, will produce reversal ; and, 

 secondly, certain tissue-modifications similar to those which 

 we have observed during the progress of fatigue. It is clear 

 that with slight tissue-modification the critical value of the 

 E.M.F. at which, under normal conditions, reversal of polar 

 effects would take place, will be lowered. This, the experi- 

 ments on Mimosa just described clearly show ; for in them 

 we see that reversal has set in at the relatively low E.M.F. of 



P 



