20() K ADI XriON lilOLoGY 



peroxide can ai'couiil for at least a part of the effects at very high doses. 

 He shows that both the percentage of eggs fertilized and the time of first 

 ciea\'age were affected by treating sperm with hydrogen peroxide; in about 

 the concentration in which it is found in heavily irradiated sea water. 

 Contrary to the conclusion of Evans ct al. (1942), cleavage delay is there- 

 fore not necessarily a direct effect. Evans (1947) believed that the effect 

 of hydrogen peroxide was slow, so that by irradiating a dilute suspension 

 of sperm and removing the sperm ([uickly to fresh medium all or almost 

 all this effect could be eliminated. The peroxide effect appears to be dif- 

 ferent from the "activated water" effect in a number of respects such as 

 the effect on cleavage as well as on fertilizing power of the sperm. Conse- 

 quently, both these mechanisms of indirect action through the medium 

 have to be taken into account. 



Barron et al., (1949a, b) have also studied this problem with Arbacia 

 sperm by using respiration of the sperm to measure the radiation effect. 

 Diluted sperm (1 -.200) showed that X rays, even at doses as low as 100 r, 

 caused a measurable inhibition of respiration. These investigators 

 pointed out that hydrogen peroxide in low concentration increased 

 respiration and so the effect at low doses could not be caused by this sub- 

 stance. Furthermore, they found that sea water exposed to 100,000 or 

 200,000 r had a marked inhibitory effect on sperm respiration, and that 

 the addition of catalase to the water before addition of sperm had no 

 effect. Finally, they were not able to demonstrate any hydrogen 

 peroxide in sea water exposed to 200,000 r although such water inhiljited 

 respiration by about 60 per cent. They believe that stable organic 

 peroxides which may be formed in sea water can account for this and other 

 cases in which irradiated fluids have an effect. 



Attention should be drawn here to the finding of Stone and his coworkers 

 (Wyss et al., 1950) that mutagenic substances are formed by ultraviolet 

 irradiation of culture medium. 



In summary, there is a good deal of evidence that stable substances 

 which produce biological effects can be formed in the medium as a result 

 of irradiation. However, these substances do not appear to be formed in 

 sufficient concentration to account to any large extent for such effects as 

 death of paramecia, since medium treated with a dose which would have 

 been lethal to the animals is not in itseff lethal. Evans et al. (1942) have 

 presented evidence for the formation of very unstable substances in the 

 medium; and such substances may be responsible for at least part of the 

 effects produced. This group was unable to find evidence that cleavage 

 delay was affected by such unstable substances. It can be concluded that 

 stable and unstable substances produced in the medium all play a role 

 but that direct effects in the cells are probably also involved. The rela- 

 tive importance of these diverse pathways of action of the radiation m^ay 

 not be the same for different effects. 



