THREE FIQURES
That continuously maintained bioelectric potentials are conditioned by cell metabolism would appear to be generally acknowledged (Dean and Gatty, '37; Barnes, '39; Blinks, '40). There is less agreement, however, as to the nature, extent and intimacy of the relations involved. The importance of the elucidation of these relations may be summed up in the statement that neither our understanding of the role of the electrical energy in the biological economy nor our use of the electrical changes as indices of physiological processes can be complete in the absence of detailed knowledge of the mechanism of production and variation of electromotive force in the living systems concerned.
The only thoroughgoing attempt to formulate the relationship between metabolism and cellular electromotive force is embodied in Luiid 'S ( '28, '31) oxidation-reduction theory, wherein the electroniotively active materials are pictured as being continuously created and destroyed in the chain of chemical events constituting the respiratory process, but under constant conditions maintaining flux equilibrium concmtrations. The equations for E.M.F. derived from the standpoint of the kinetics of the respiratory reactions (Marsh, '35) satisfy the requirements of many experimental observations. The respiratory process was schematized as follows: the reductant was assumed to be mobilized reversibly f rom some store, dehydrogenated to forin the oxidant with the uptake of oxygen at a rate determined by the oxygen pressure and the concentration of reductant, and the oxidant destroyed by further transformation at a rate proportional to its concentration. The eqpations predict that the E.M.F. will increase from zero, pass through a maximum and return to zero as the oxygen pressure is increased from zero without limit. This has been verified for the onion root tip (Marsh, '37) and the principle appears t o operate in the effect of light intensity upon the E.M.F. of Valonia ventricosa (Marsh, '39).