Frog erythrocytes in Ringer's solution were exposed to ultraviolet radiation and then followed in camera lucida drawings for changes in shape and dimension. Cell thickness was found to increase while cell width remained constant throughout the period prior to hemolysis. The cell shortened and bulged at the ends during the middle third of the prolytic period while a region around the cell center remained constricted. When this constricted region gave way, the cell became spherical and hemolyzed. Cell volume as calculated from the cell's dimensions increased linearly with time throughout the prolytic period to hemolysis then dropped rapidly to a constant value somewhat higher than the original cell volume. These changes in shape and volume are consistent with a colloid osmotic type of hemolysis but with other factors acting to limit the rate of swelling and the forms assumed during the swelling process. The relationship between the time of hemolysis and the cell surface area exposed to the ultraviolet is discussed as it applies to the site of ultraviolet damage.

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