A STUDY OF THE OSMOTIC BEHAVIOR OF THE HUMAN ERYTHROCYTE * t

Despite many previous studies of the osmotic properties of erythrocytes, unequivocal answers have not been given to two important questions: 1) Is the erythrocyte in osmotic equilibrium with its normal surrounding fluid? 2) When the osmotic properties of the surrounding fluid are varied, does the erythrocyte gain or lose water to the extent necessary to remain in osmotic equilib-rium with the new surroundings-that is, does the erythrocyte behave as a perfect osmometer over a wide range? Previous work related to these questions has been of two general types: measurements of changes of volume of the erythrocytes as the osmotic concentration of the extracellular phase was altered; and measurements of one or more of the colligative properties of the solutions involved. The present study is of the latter type. The osmotic behavior of the normal human erythro-cyte has been investigated over a wide range of concentrations by a cryoscopic method and a method for measuring the melting point of micro-scopic samples. The results give affirmative an-swers to both of the above questions and illustrate some of the difficulties which may be expected in studies of osmotic properties of any tissues. *This investigation was supported in part by a De