478 E. J. LUND 



In the present paper evidence will be presented, which it is 

 believed amounts to a proof of the existence of a normal difference 

 of electrical potential in the living tissue of the stem of Obelia, 

 the occurrence of which was suggested by the experiments in 

 the previous paper. 



EXPERIMENTAL 



The galvanometer which was used to detect the currents ob- 

 tained by leading off from different levels of the stem, was a 

 Leeds Northrup instrument of somewhat more than one thou- 

 sand megohm sensitivity.^ Under the conditions of the proce- 

 dure in the experiments, it was difficult or impossible to make 

 non-polarizable Zn-ZnS04 electrodes which maintained a per- 

 fect iso-electric condition. Consequently, the simple arrange- 

 ment of a copper wire inserted in a bent tube filled with sea- 

 water, as shown in figure 1, was used as a readily washable 

 electrode. The two electrodes used gave a sufficiently constant 

 difference of potential for the purpose of the present experiments. 

 The same pair of electrodes were used in all the experiments.^ 



Suppose now that the electrodes are placed at a definite dis- 

 tance apart and a piece of stem is placed upon them such that 

 the ends rest in the drops of sea-water as shown in figure 1. 

 The galvanometer will show a certain deflection due to the P.D. 

 between the electrodes. If, now, the stem is reversed in its 

 position and the galvanometer deflection is identical with the 

 first, then ob\dously the current is the same. But, if the de- 

 flection is less, then either one of two possibilities exists: 1) An 

 inherent P.D. exists in the stem such that it opposes the P.D. 

 between the electrodes or, 2) the ohmic resistance is greater in 

 the latter position than in the first position. If the first of these 

 possibilities is the correct interpretation, then ob\dously the 

 deflection with the stem in the first position is greater than would 

 occur if no P.D. inherent in the stem existed between the ends 

 of the stem. The correct measure of the current due to the 



1 The instrument was kindly loaned by Prof. H. L. Brakel, of the Department 

 of Physics of the University of Washington. 



2 It is apparently impossible to reproduce a Cu-CuS04 electrode. 



