The Red Cell as an Osmometer

For at least fifty years there has been doubt as to whether the mammalian erythrocyte, a supposedly simple cell with a membrane only some 150 A thick (Fricke, Parker, and Ponder, 1939), and containing a solution of salts, hemoglobin, and perhaps some kind of internal "stroma", adapts itself to changes in osmotic pressure by the transfer of water alone, i.e., as to whether it is a "perfect osmometer". The early literature is so confused as to be scarcely worth reviewing again (see Ponder, 1934), and so I will state the problem, and even the dilemma, in its simplest terms, and then consider the solutions which have been proposed.