DISCUSSION 239 



which protect the system from alteration. If a biological system is 

 found to be resistant to the action of ionizing radiations in vitro, there 

 is reasonable certainty that it will also be resistant on irradiation in 

 the living cell. Besides these complicating factors of the action of the 

 environment, the complexities increase when mutual interactions are 

 taken into consideration, to wit, the metabolic dynamic equilibrium 

 which allows for continuous resynthesis of the destroyed products, salt 

 and H+-ion effects, hormonal effects, oxygen tension effects, etc. 



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DISCUSSION 

 Tahmisian: 



Several years ago Barron and his coworkers found that small concentrations 

 of sulfhydryl reagents increase the oxygen uptake of sea-urchin sperm. When 

 we found that the oxygen uptake of embryos increased on irradiation with 

 25,000 r, we wanted to test whether the sulfhydryl groups were oxidized. In vivo, 

 however, when the sulfhydryl groups were tested with the nitroprusside test, no 

 change could be detected after irradiation even with doses up to 200,000 r. It 

 is very important, as Dale and Barron show, that damaging of molecules in vitro 

 can be brought about by irradiation. But making conjecture that this is what 

 happens in vivo becomes very dangerous, so that these in vitro experiments must 

 also be substantiated experimentally in vivo. There is a gradual diminution in 



