||"The Cl distribution in E. coli during the logarithmic phase cannot be demonstrated to be the result of either an active or a passive transport mechanism in the absence of a direct measurement of the transmembrane P.D. [potential difference] However, as is seen in Table II link the ratios [Na]i/[Na]o and [K]i/[K]o in the logarithmic phase differ markedly from the value for [Cl]o/[Cl]i. If one assumes, for each ion, that the intracellular and extracellular ionic activity coefficients are equal, the following equilibrium potentials can readily be calculated: E[K] = 61 log ([K]o/[K]i) = -100 mv: E[Na] = 16 mv: E[Cl] = -29 mv. One may conclude from these data that active transport processes are responsible for the steady-state distributions of at least two of these ions. Although [investigators] cannot rule out the possibility that Cl is actively transported by E. coli, the assumption that Cl is distributed passively is supported by the observation that the [Cl]o/[Cl]i ratio is constant over a wide range of extracellular Cl concentrations."