252 Discussion 



without hydrogen, you get a family of curves for hydrogen peroxide 

 yield against oxygen concentration. With low doses you get the equilib- 

 rium yield at low oxygen concentrations, whereas with a high dose you 

 don't get the equilibrium yield until the oxygen concentration is high. 

 If you start with 100 per cent oxygen, then add hydrogen, the equilib- 

 rium yield rises sharply, for low doses, and is independent of hydrogen 

 concentration over a wide range of hydrogen-oxygen mixtures. As you 

 decrease the oxygen to zero and increase hydrogen to 100 per cent the 

 yield stays constant and falls sharply to zero as oxygen concentration 

 falls to zero. With higher doses the range of mixtures over which you 

 get constant yield becomes much smaller, and the relative proportions 

 of hydrogen and oxygen become critical. With low doses, however, you 

 get a very wide range of mixtures with which yield is unaltered. 



Swanson : What do you mean by low doses ? What range ? 



Alper: 10-20,000 r with the methods he has used up to now, but 

 presumably this range would be extended if one could use lower doses. 



Swanson: In the hundreds? 



Alper: It depends on how low he has gone with the oxygen. I don't 

 know what the actual range was. This doesn't mean that hydrogen 

 peroxide is constant. 



Howard: Prof. Swanson, you say that if you add hydrogen to an 

 oxygenated system the frequency of aberrations is increased. This is 

 different to what we found with bean roots in which we got less damage 

 in presence of hj^drogen, even when oxj'^gen was also present. 



Swanson : I am aware of that. The study done by Mr. Merz was on the 

 microspores of Tradescantia. I think that the gases were accurately 

 controlled. There is some danger, of course, of a flash-back, but we 

 managed to avoid it. We got practically the same results regardless of 

 what we added in the way of hydrogen, making certain at all times that 

 the oxygen was at least 20 per cent. 



Howard: Did you have hydrogen under pressure? 



Swanson: No, this was just the flowing gas, under no pressure. 



Haddow: Am I right in believing that maleic hydrazide has no effect 

 on animal cells ? I think maleic hydrazide certainly has no effect what- 

 ever of these kinds on animal cells. 



Swanson : I only know that McLeish reported that it was ineffective on 

 onion chromosomes where no visible heterochromatin is demonstrable, 

 but this is not entirely correct because it will break them very effectively 

 if you adjust the temperature and the pH. Maleic hydrazide, therefore, 

 is not a mutagen restricted in its activity to heterochromatin, although 

 that is the preferred site of action. 



Haddow: We have come across this in a practical way in connection 

 with maleic hydrazide which, it was believed, might possibly be car- 

 cinogenic. But it is certainly not a strong carcinogen. 



Swanson : I wonder whether this would be true if the data were taken 

 over a period of time, as with the diepoxide. We assumed that there was 

 no oxygen effect with the diepoxides, but if one examines the cells at a 

 later time after treatment, at least with the metabolic inhibitors, one 

 does observe a decided effect. 



