MUTAGENS OF POTENTIAL SIGNIFICANCE 225 



a test that can be made without a great deal of effort. A test of the 

 effect of a particular chemical on the dominant lethal rate could be 

 completed in a few weeks. 



Atwood: If that were true, and the estimate of 200,000 r or 20,000 r 

 or something of that sort were correct, is it also true, then, that coffee 

 drinkers would be sterile? They may be sterilized by dominant lethals. 



Russell: Yes, if it worked this way. 



Atwood: They would be sterile several times over. 



Russell: In the Drosophila data that you have summarized, it looks 

 as though the mutagenic effect reported from the treatment of adult 

 males occurs before the seventh day matings. In other words, you are 

 getting caffeine-induced mutations when there is no replication, and 

 not getting them after the seventh day matings when the cells involved 

 may have gone through replication. 



Goldstein: No, this injection experiment was not chronic administra- 

 tion. There was a single injection of caffeine in the one-day-old male. 



Russell: Yes, but I was referring not to the administration of the 

 caffeine, but to the germ cell stages that were exposed to it. Matings 

 made up to the seventh day would include cells that had been exposed 

 in which stages? 



Glass: Spermatozoa and spermatids; nothing earlier. 



Russell: So all the effect produced, if what was observed was indeed 

 a real effect, must have occurred in cell stages where no replication 

 was going on. Then the effect ceases for later broods of offspring. The 

 summary says "beyond the seventh day." 



Goldstein: It was carried on to the eleventh day. 



Russell: Eleven days may not be long enough to include sperma- 

 togonia. 



Glass: One must carry the testing beyond the tenth or eleventh day 

 to test cells that were spermatogonia at the time of treatment. 



Russell: Matings made between seven and eleven days will, however, 

 involve cells that were exposed as spermatocytes and possibly some 

 exposed as spermatogonia. Thus, the reported mutagenic effect of 

 caffeine occurred in cells in which there was no replication, and was not 

 detected in cells in which there was replication ! 



Neel: I must say that I'm getting a great deal of wry amusement 

 from all this. I am one who has refused for some time to be pushed 

 into calculations about the genetic effects of radiation on man, and 

 have been vigorously criticized by a good many of my colleagues for 

 dragging my feet. Now, what's happened? 



Lederberg: I would like to react to Avram with a statement of 



