A B S T R A C TIn the negative EOG-generating process a cation which can substitute for Na + was sought among the monovalent ions, Li +, Rb +, Cs +, NH4 +, and TEA +, the divalent ions, Mg ++, Ca ++, Sr ++, Ba ++, Zn++, Cd++, Mn ++, Co ++, and Ni ++, and the trivalent ions, A1 +++ and Fe II z. In Ringer solutions in which Na + was replaced by one of these cations the negative EOG's decreased in amplitude and could not maintain the original amplitudes. In K+-Ringer solution in which Na + was replaced by K +, the negative EOG's reversed their polarity. Recovery of these reversed potentials was examined in modified Ringer solutions in which Na + was replaced by one of the above cations. Complete recovery was found only in the normal Ringer solution. Thus, it was clarified that Na + plays an irreplaceable role in the generation of the negative EOG's. The sieve hypothesis which was valid for the positive EOG-generating membrane or IPSP was not found applicable in any form to the negative EOGgenerating membrane. The reversal of the negative EOG's found in K +-, Rb +-, and Ba++-Ringer solutions was attributed to the exit of the internal K +. It is, however, not known whether or not C1-permeability increases in these Na+-free solutions and contributes to the generation of the reversed EOG's.The ionic mechanisms underlying the generation of the electro-negative and positive "electro-olfactograms" (EOG's) have been studied in previous papers (Takagi and Wyse, 1965;Takagi, Wyse, and Yajima, 1966;Takagi, 1968; Takagi, Wyse, Kitamura, and Ito, 1968). Briefly, the results showed that the negative EOG's primarily depend upon the entry of Na+ and the simultaneous exit of K +, and that neither Li +, tetraethyl a m m o n i u m (TEA+), choline +, hydrazine, nor sucrose can substitute for Na+; the positive EOG's primarily depend upon the entry of CI-and the simultaneous exit of K +, and three anions, Br-, F-, and H C O~ can substitute for C1-.
