;j()4 |{ ADl A'PIOX IIIOLOGY 



radiation. Alpatov and Xastiukova (iy34(') found that the effect of 

 ultraviolet on Paramrriiim was intensified by exposure to slifi;htly unfa- 

 \-oral>le temperatures after irradiation, the least effect hein^ evident when 

 the animals were irradiated at temperatures near the middle of tlu; \ital 

 range. They suggest tliat these changes in sensitivity may he related to 

 protoplasmic viscosity. In another paper (1934h) they report that 

 sodium sulfate and electrical stimulation, both of which increased the 

 viscosity, decreased the effect of ultraviolet while potassium thiocyanate 

 and mild narcosis, which decreased the viscosity, increased the sensitivity 

 to ultraviolet. On the other hand, Wilbur and Recknegel (1943) have 

 shown that treatment of Arbacia eggs with potassium citrate (0.35 M) 

 only slightly decreased the retardation of cleavage by X rays, whereas 

 addition of calcium or magnesium to the sea water had no effect at all. 

 All these treatments affected the viscosity of the egg. These investiga- 

 tors also report that doses of X rays (30,000 r) which markedly affected 

 the rate of cleavage had no detectable effect on viscosity. They con- 

 cluded that changes in ionic composition and viscosity cannot be impor- 

 tant factors in division delay by X rays. Zirkle (1936) has shown that a 

 high carbon dioxide content in the atmosphere at the time of irradiation 

 increases the sensitivity of Paramechim to the division-retarding effects of 

 X rays. Hutchings (1948) reported that Arbacia eggs suffer cleavage 

 delay when briefly exposed to 36°C^ 10 min after insemination. She 

 found that the cleavage delays produced by this temperature and by 

 2537 A ultraviolet were additive, or nearly so, when the eggs w^ere exposed 

 to the high temperature either before or after the irradiation. 



The phenomenon of photoreactivation has been studied for clea\'age 

 delay in sea urchin eggs exposed to ultraviolet by Blum . . . Robinson 

 (1949); Blum, Loos, and Robinson (1950); Blum, Robinson, and Loos 

 (1950); Marshak (1949a, b); and Wells and Giese (1950). It has also 

 been found for di\'ision delay in ultraviolet-irradiated P. aurclia by Kim- 

 ball and Gaither (1951). The subject will not be discussed further here, 

 since it will be reviewed in detail by Dulbecco in Chap. 12 of this volume. 



Differences in sensitivity between various strains and species have 

 been reported by several investigators. Alpatov and Nastiukova 

 (1934a) found distinct differences in sensitivity to ultraviolet between 

 P. caudatum and P. bursaria. Giese and Reed (1940) made an extensive 

 study of different species and stocks of Paramecium and found considera- 

 ble difference in their sensitivity to the division delay produced by ultra- 

 violet. They also found that starved pai'amecia were more susceptible 

 than well-fed ones. Giese (1946b) reported a wide range in sensitivity to 

 ultraviolet in the eggs and sperm of different marine invertebrates. The 

 echinoderms, whose eggs have indeterminate cleavage, are mature when 

 shed, and cleave radially, showed a consideral)le difference in sensitivity 

 between egg and sperm, and cleaved abnormally only when given high 



