Comparative Ultraviolet Sensitivity of Regeneration in the Genus Blepharisma*

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Abstract
SYNOPSIS. Regeneration of different stocks of Blepharisma representing several species is retarded to different degrees by identical doses of UV radiation (2654 Å). UV susceptibility of regeneration is greater in some small‐sized stocks than in some large‐sized stocks and in stocks with a lesser amount of pigment than in the more deeply pigmented ones. For the same dose regeneration is retarded more by low‐intensity than by high‐intensity short wavelength UV radiation. The UV action spectrum for regeneration delay in the Rao A stock, determined with UV of similar intensity at various short UV wavelengths, resembles absorption by nucleoprotein more than ahsorption by other cell constituents. Post‐regeneration division is also retarded by UV, and the aotion spectrum for division delay resembles that for regeneration delay, except that 2801 A is relatively more effective in retarding division than regeneration. Possible explanations for the results are considered.