1 68 COMPARATIVE ELECTRO-PHYSIOLOGY 



saline. In very obstinate cases, however, I succeeded in 

 eliminating all differences by subjecting the electrodes to 

 cyclic variations of alternating electro-motive force. By 

 means of a Pohl's commutator, without cross-bars, the 

 electrodes were put in connection with an alternating source 

 of E.M.F., and with the galvanometer intended to test 

 the resulting variation in the E.M. difference, by turns. 

 A small hand-driven alternating-current generator was used 

 for this purpose. The speed of rotation of this machine 

 was gradually raised to a maximum, and afterwards as 

 gradually slowed down. Thus at each cycle the electrodes 

 were subjected to ascending and descending intensities of 

 alternating electro-motive variations. The effect of such cyclic 

 changes, in diminishing the existing electro-motive difference 

 between a pair of electrodes, specially selected for carelessness 

 of preparation, will be clearly seen from the following tabular 

 results : 



It will thus be seen that, after a very short time of this treat- 

 ment, the two electrodes were rendered iso-electric. 



I next proceeded to determine the distribution of elec- 

 trical potential in the various portions, living and dead, of 

 the leaf. In order to remove any accidental strain, the leaf 

 was placed in tepid water, and kept there for about half an 

 hour, till the water was cooled to the surrounding temperature. 

 The experiment was then carried out, in the manner already 

 described, and the following tabular statement shows the 

 results obtained. The electrodes, it will be remembered, were 

 placed successively at points 5 mm. apart from each other, 

 along a radial line proceeding from the dead tissue to the 

 living, the first point being taken as zero : 



