Physiological "Polarity" and Electrical Polarity. 343 



changes accompanied by the escape of body fluids at the cut end. 

 Since, when the electrodes are on two transverse sections, the one 

 that is more recently cut is of a lower potential than the other, it 

 would appear that the causes that determine the fall of potential 

 are such as decrease in the course of a short time. The fluids 

 that escape from the cut end dry rather rapidly, whereas the tissue 

 cells, breaking down, are not built up for several days. The first 

 fall of potential, then, is probably largely due to escape of blood 

 or other fluids from the section, while the slighter permanent effect 

 may be due to the breaking down of tissue cells. When there 

 was but a short time between the two cuts the lower potential did 

 not always occur at the fresher one, which may have been partly 

 because fresh fluids were still coming from the earlier section. In 

 the anterior half of the worm, also, there was great irregularity, 

 which may be partly due to difi^erent digestive fluids at different 

 regions of the digestive tract producing varying electrical activi- 

 ties. 



The differences of potential between two transverse sections are 

 probably a resultant of the factors that cause difference of poten- 

 tial between a section and a surface. If a piece be cut out from 

 an earthworm by two transverse sections, there will be a difference 

 of potential between each end and the surface between the ends. 

 If the differences of potential between each end and the surface 

 are equal and opposite they will balance one another, and there 

 will be no difference of potential when electrodes are applied to 

 the two ends. If, however, the differences of potential between 

 the two ends and the surface are unequal, their resultant will de- 

 termine a difference of potential between the two ends. This is 

 illustrated by experiment 10. 



Experiment 10. Lumbricus terrestris. Short piece. The zero 

 point of the galvanometer was 28.6, and the electrodes registered 

 slightly above this at the beginning of the experiment. The read- 

 ings were as follows : 



(a) One electrode applied to anterior end, the other to the 



middle of the piece 25.0 



(b) One electrode applied to posterior end, the other to the 



middle of the piece 30.8 



