Diffusion constant for CO₂ through urinary bladders of cats

Diffusion of CO₂ through tissue was studied by a simple technique which avoided error due to unstirred layers in a bathing medium and which accounted for CO₂ production in the tissue. The practice of dividing permeation data by solubility to yield the customary Fick diffusion coefficient (units of cm² min^-1) is valid only in a homogeneous, isotropic substance, which tissue probably is not. Therefore the results are presented here in terms of the permeation coefficient, or Krogh's diffusion constant (units of cm² · min^-1 · atm^-1). The value at 25 °C was 5.0 × 10^-4 cm².min^-1.atm^-1, and there was no appreciable change when metabolism was depressed after the tissue had been kept for four days in a deep freeze and then thawed.