368 LIBBIE H. HYMAX. 



elsewhere (Hyman, '18) and further papers upon the subject will 

 appear shortly. Briefly it is believed that chemical differences 

 are as a rule responsible for these permanent differences in 

 potential and that such chemical differences arise in the final 

 analysis through differences in metabolic rate at different levels. 



The existence of such a difference in electrical potential 

 along the axis of Tubularia was discovered by Mathews ('03). 

 Mathews found that the hydranth is negative to any region of 

 the stem and that distal levels of the stem are negative to 

 proximal levels. He correctly attributed these potential differ- 

 ences to differences in metabolic activity. 



I have repeated these experiments on Tubularia and verified 

 all of Mathews' statements. A galvanometer constructed on 

 the principle of the D'Arsonval galvanometer and put out by 

 the Leeds and Northrup Company was used. Although not as 

 sensitive as some other types of galvanometers in use, the 

 instrument was found adequate for the purpose. Non-polariz- 

 able electrodes were employed, made in the usual way of the 

 glass tubes from medicine droppers, packed at the small end with 

 kaolin paste made with sea-water, and filled at the other end with 

 saturated zinc sulphate solution. Zinc rods, amalgamated with 

 mercury, dipped into the zinc sulphate solution, and were con- 

 nected by copper wires with the binding posts of the galvanom- 

 eter. Small rolls of hard filter paper were thrust into the ends 

 of the electrodes and the stems to be tested placed on these. 

 These filter paper rolls \vere kept soaked with sea-water. Al- 

 though such electrodes are made as nearly alike as possible, 

 there is almost always some difference of potential between them. 

 Such difference increased with use so that it was necessary to 

 renew parts of the electrodes or to make wholly new ones at 

 frequent intervals. The existence of a potential difference be- 

 tween the two electrodes of course makes it impossible to obtain 

 an absolute value of the amount of current originating from the 

 organism; but absolute values were not desired in the present 

 experiments. It was my purpose merely to discover which 

 regions of the organism were electronegative as compared with 

 other regions. 



In performing the experiments isolated stems of Tubularia in 



