2. Assuming that alveolar milk has the same concentration as teat milk, the intracellular concentrations were calculated to be K 115, Na 42 and C1 66 m-equiv. 1-1 intracellular water.3. Intracellular concentrations were also calculated in slices incubated in Krebs-bicarbonate medium plus glucose. There was a large increase in the sucrose (E.C.) space and a rise in total tissue [Na] and [Cl]. On the assumption that the medium had equilibrated with the milk space as well as the E.C. space, the calculated I.c. concentrations of Na (43 m-equiv.