Physiological "Polarity" and Electrical Polarity. 339 



at the opposite end of the worm. If, however, resistance varied 

 in different parts of an unhomogeneous tissue, the difference of 

 potential observed between two points would be a resultant be- 

 tween a tendency to a regular rise of potential and an irregular 

 distribution of resistance, and the recorded distribution of poten- 

 tial would, therefore, be irregular. In point of fact, however, as 

 mentioned above, other causes of irregularity may be added to 

 those due to resistance, and many arrangements of potential were 

 observed in the seventeen cases tested. 



ELECTRODES APPLIED TO TWO POINTS ON THE SURFACE. 



Experiment 5. Lumbricus terrestris. The zero point of the 

 galvanometer was 28.6, and the electrodes deflected it to 27.9 or 

 27.8, in an opposite direction from deflections caused by the worm. 

 This experiment was made in order to see what the electrical con- 

 ditions are on the surface of the worm. Three readings were 

 taken, as follows : 



a. Earthworm cut in two at the mid- 



dle. 

 Posterior piece. One electrode on 

 the surface at the section and the 

 other on the surface, posterior to 

 the section, but near It 30.3 Posterior positive 



b. Same worm. Short piece cut from 



posterior half of animal. 

 One electrode on the surface at the 



anterior section, and one on the 



surface posterior but near 33.9 " " 



One electrode on the surface at the 

 anterior section, and one on the 



surface at the posterior section. 35.0 " " 



The direction of current was the same as would be expected if 

 one electrode were applied directly to the cut end, and the other to 

 the uninjured surface near the end. On the assumption that at 

 any level the conditions of the surface fairly represent those in the 

 interior of the worm, by testing the distribution of potential at 

 the surface of an uninjured specimen It may be possible to get some 



