DISCUSSION 



CO, KCN, hydroxylamine and azide. Urethane did not abolish or diminish 

 the ' Og-effect '. 



The mode of the- effective poisons in their role as respiratory inhibitors 

 is known. They all block hydrogen transfer through the respiratory enzymic 

 system by combining with oxidized cytochrome a-j and stabilizing the remain- 

 ing respiratory enzymic chain in the reduced form. Taking this mode of 

 action as a guide in advancing a possible explanation for the ' Og-effect ' in 

 irradiation, it is suggested, at least for this bacterium, that the enhancement 

 of irradiation damage (1) involves the enzymic respiratory mechanism, 

 (2) requires at least part of the enzymic respiratory chain to be in the oxi- 

 dized form during irradiation. This makes it possible, that the impedance 

 has been caused by a reducing agent. 



DISCUSSION 



F. H. SoBELS : I was interested to hear about Laser's observation that potassium 

 cyanide exerts a protective effect against X-radiation in bacteria in view of the 

 opposite resuhs recently obtained by myself in Drosophila. Here injection of potas- 

 sium cyanide prior to X-radiation significantly increases the mutation rate as 

 compared to that induced by the same dose of X-rays alone. Similarly King, 

 Schneiderman and Sax showed that carbon monoxide pretreatment increases the 

 frequency of X-ray induced chromosome aberrations in Tradescanlia. It seems as if 

 the exactly opposite results of cyanide on radio-sensitivity spring from another 

 metabolic situation in the different experimental materials used. 



69 



