REVERSED POLAR EFFECTS IN LIVING TISSUES 207 



Under high E.M.F. — at the A stage — both anode and kathode 

 excite at make ; at break there is occasional excitation at 

 either anode or kathode. Under excessively high E.M.F. — at the 

 B stage — the anode excites at make and the kathode at break. 



Without this addition the law of polar excitation is in- 

 complete ; and I shall have occasion, in my work on the 

 Electro-Physiology of Plants, to show its application in 

 explaining certain excitatory electromotive phenomena which 

 would otherwise have remained obscure. 



Investigation on polar effects by death-response. — 

 I have already explained in Chapter XV. that the death- 

 point of an excited tissue is lowered below the normal. This 

 made it possible to devise a test by whose means it might be 

 determined which of the two electrodes produced excitation. 

 Thus, on taking two similar petals of Passiflora, and making 

 one anode and the other kathode, it was found with a 

 moderate E.M.F. that death-discoloration took place at the 

 kathode, at a temperature of 4 C. lower than at the anode 

 (p. 185), thus proving that under these conditions it was 

 the kathode which produced excitation. I was now desirous 

 of finding out whether the same test could not be applied to 

 the demonstration of the reversed effect due to high E.M.F., 

 and in this connection I shall give an account of an experi- 

 ment on the coloured petals of Sesbania coccineum, the death- 

 discoloration of which occurs normally at 65 '5° C. Taking 

 two similar petals, and using the high E.M.F. of 220 volts, 

 I found on sending a current that death-discoloration took 

 place at the anode, at 6o° C, that is at 6|° below the normal. 

 The discoloration point of the kathode was also lowered, 

 but only slightly, being 2^° below the normal. We thus see 

 that with a high E.M.F. it is the anode which is more ex- 

 citable at make. It is clear from this that the reversal of the 

 normal polar effect has set in, the anodic excitation being 

 considerably predominant. 



Reversal of polar effects as due to fatigue or tissue- 

 modification. — It has now been demonstrated that an exces- 

 sively strong E.M.F. is one of the conditions by which the 



