The rate of penetration of CO2 into living cells of Valonia has been studied at high and low pH values.

The time curve of penetration appears to be of the first order but with a "velocity constant" which falls off from the start.

The evidence indicates little penetration of ions. This is shown by (a) the similarity of velocity "constants" at high and low pH values, (b) the rate of penetration, which remains constant as long as the external concentration of undissociated CO2 remains constant no matter how much the concentration of ions varies.

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