THE COMBINED EFFECT OF ULTRAVIOLET IRRADIATION AND HEAT UPON CLEAVAGE OF SEA URCHIN EGGS

¹ Department of Surgery, Western Reserve University School of Medicine and Cleveland Metropolitan General Hospital, Cleveland 9, Ohio

1. Thermal treatment (36° C. Arbacia; 31.4° C. Strongylocentrotus) applied to sea urchin eggs in graduated exposures causes a delay in first cleavage that is roughly proportional to the exposure.

2. Graduated intensities of 254 mµof ultraviolet light produce a delay in first cleavage that is less pronounced with increasing intensities of light.

3. Treatments involving both ultraviolet irradiation and heat retard the first cleavage of sea urchin eggs more than either agent alone.

4. Curves of cleavage delays of Arbacia eggs caused by combined ultraviolet light and 36° C., either one serving as the major physical agent and the second as the minor physical agent, show no statistically significant difference from a hypothetical curve representing a sum of the two single-agent delays.

5. Although there is no evidence that ultraviolet irradiation preceding heat causes an exaggerated injury, which application of the same agents in reverse order fails to do with Arbacia eggs, there is an indication that such sensitization tends to occur in Strongylocentrotus eggs pretreated with 254 mµ of ultraviolet radiation and then subjected to heat at 31.4° ± 0.5° C.

6. Strongylocentrotus eggs pretreated to a temperature of 31.4° C., followed by exposure to ultraviolet irradiation (254 mµ), show significantly less delay in achieving first cleavage than eggs subjected only to a temperature of 31.4° C.