Minutes 



Textfigurb 15. — Effects of oxygen on bioelectric potentials 

 in Halicystis. G)-aphs showing fall of P.D. in impaled cells of H. 

 ovalis, when 0.2 per cent O2 in N2 is substituted for 2 per cent 

 Oi (each bubbling continuously). In A the fall of P.D. in 0.2 per 

 cent O2 is rather slow the first time, possibly because air had not 

 been thoroughly exhausted from the vacuole, although 2 per cent 

 O3 had been bubbled for Yo hour previously (without reducing the 

 P.D. below the air value) . After recovery in 2 per cent O2, the 

 second fall in 0.2 per cent O2 is faster, and reaches a lower level. 

 Note the downward cusps preceding recovery in each admission of 

 2 per cent O2. 



In graph B another more sensitive cell is shown. This had 70 

 mv. P.D. in aerated sea water, which fell to 60 mv. in 2 per cent 

 O2. The fall on bubbling with 0.2 per cent O2 is much faster and 

 the P.D. drops to 18 mv. Readmission of 2 per cent O2 promptly 

 restores the P.D. The reproducibility of the curves and of the 

 levels reached in each case are noteworthy. 



Ordinates are P.D. in millivolts, the sign, outside of cell posi- 

 tive. Arrows indicate change of the gases bubbled. (From L. R. 

 Bunks, Darbie, and Skow, 1938). 



