MUTAGENS OF POTENTIAL SIGNIFICANCE 219 



with his assumptions and the calculations which follow and then ex- 

 plore what happens if we alter his assumptions along lines suggested 

 by some of the comments? 



Auerbach: May I just ask Dr. Novick one question? Couldn't your 

 data be explained if one assumes that, dependent on the length of 

 generation time, you have a constant fraction of this during which 

 synthesis takes place? 



Novick: Yes, of course. I don't say that mutation is produced at 

 any time. 



Auerbach: So it could be expressed as a fraction of generation 

 time. 



Novick: It could very well be. 



Auerbach: That might apply to human cells, too? 



Novick: I think it would make no difference. 



Goldstein: I don't think there is any question about spermatogonia 

 division here. I think this is a red herring. We're arguing about some- 

 thing else. 



Lederberg: Did somebody propose that spermatogonia would not 

 multiply? 



Goldstein: I don't know. 



Novick: Yes, in assumption 6a. 



Goldstein: I don't think that is implied. 



Novick: It is explicit. 



Goldstein: Where this does come in, however, is in relation to the 

 female, where the evidence, as we have heard, is that germ cell 

 division does not continue beyond the fetal period. One would expect 

 that in the female, however, agents which acted with time regardless of 

 the process of cell division would still be effective. However, let's go 

 on. 



What we do next is to take Novick's data on the effect of 150 mg/1 

 of caffeine which produced, in addition to the spontaneous rate, 17 X 

 10"^ mutations per hour per cell in the chemostat, at a generation time 

 in those experiments of about 5.5 hours. In the same experiments, 90 r 

 radiation per hour had the same effect. 



First, we reduce the concentration by a factor of just over 100 to get 

 it down to the level to which the average exposure in man corresponds. 

 On the assumption of a linear dose relationship, this would give us 

 1.5 X 10"^ mutations per hour per cell in man. Since the data refer to 

 a single gene, and I want to find out the total probability of any muta- 

 tion in man, I have to multiply this by an estimate of the total 

 number of genes in man, which I have taken as 10^. This gives 1.5 X 



