36 MUTATIONS 



merit with P^^' does not occur until — what is it — two months after 

 therapy. 



Atwood: Yes. The reason for that is the lifetime of the peripheral 

 cell. 



Neel: Precisely. That's what I was getting at. So the pulse has to 

 be viewed in relation to the total red cell count for a quantitative 

 treatment. 



Lederberg: The pulse that we are speaking of may not be influencing 

 the production of fully chromic, euchromic erythrocytes; that is, you 

 may be impairing the capacity to form surface antigen in a fraction 

 of cells, but not impairing the production of hemoglobin in most of the 

 cells. 



Atwood: Yes, I see. 



Lederberg: Only later on have you hit those cells that were starting 

 to make the hemoglobin at the time you put in the pulse of P^-. Then, 

 your anemia comes in. 



Atwood: You remember, this peak came down again well within the 

 lifetime of the peripheral erythrocyte, which is about 100 or 120 days. 

 This means that the kind of cell that makes up this peak must have 

 a short lifetime. 



Lederberg: Or else it is finishing up the job. Perhaps these cells are 

 now maturing; in other words, what you are seeing here is delayed 

 maturation rather than interrupted maturation. 



Atwood. You mean delayed until after they are in the peripheral 

 circulation? 



Lederberg : Yes. 



Atwood: This would be unexpected. 



Lederberg: Yes. Do you know that they are not reticulocytes? 



Atwood: No, you're right; they may be reticulocytes. 



Cotterman: I might say that I looked at the proportion of 

 reticulocytes in the so-called Ao + mosaics which I studied, and 

 found no unusual proportion. 



Atwood: Yours were very frank mosaics, indeed, though, weren't 

 they? 



Cotterman: Yes. 



Atwood: You would suppose that with the processes of mutation, 

 when we have stem line regime and so on, you would get a marked 

 age dependence, and so, about two years ago, we took all the isotope 

 dilution experiments that had been done up to that time and plotted 

 them against the ages of the individuals. Unfortunately, we did not 

 have a very good spread of ages, especially among the young. 



