Physiological ''Polarity" and Electrical Polarity. 333 



of the electrodes. As the electrodes were found to deteriorate 

 rapidly when used, it was necessary to examine them at frequent 

 intervals, and when the deterioration became so great as to affect 

 seriously the value of the readings on the worm, to readjust the 

 parts. This could be accomplished in several ways, of which some- 

 times one and sometimes another was most effective. A fresh 

 zinc electrode could be substituted, the zinc electrodes could be 

 freshly amalgamated, or they could be polished by rubbing them 

 with sandpaper. The current could sometimes be affected by 

 moving one zinc so that a greater or less surface was immersed 

 in the zinc sulphate. Putting fresh zinc sulphate solution into 

 the tube nearly always produced a distinct effect. All these means 

 of regulation proved more or less temporary, and often, when 

 they all failed to balance the electrodes, fresh ones had to 

 be made. The electrodes in which filter-paper was used proved 

 much more constant and easy to regulate than the clay ones, and 

 if they were often renewed, it seemed safe to employ them. 



A positive deflection of the galvanometer meant that the poten- 

 tial at the right hand electrode was higher than that at the left 

 hand, i. e., the current through the galvanometer flowed from 

 right to left. Since in nearly all cases the left hand electrode was 

 placed on the worm anterior to the right hand one, a positi\"e de- 

 flection meant that the current flowed through the galvanometer 

 from the posterior to the anterior electrode. 



The electrodes were applied, sometimes both to the dorsal sur- 

 face of the worm, sometimes to the ends made by transverse sec- 

 tions through the body, and sometimes one to the surface, and the 

 other to a cut end. The results will be considered according to 

 the position of the electrodes. 



ONE ELECTRODE ON THE SURFACE AND THE OTHER ON THE 



CROSS-SECTION. 



It will be seen from the records given in the following selected 

 tables that however general certain results appear to be, never- 

 theless some individuals show irregularities. This uncertainty in 

 the results can be in part at least accounted for by the following 

 considerations. Secretions in different regions of the body, the 



