KOHN: Yes, yes. BERGE: Do you know anything about Dr. Hamilton? KOHN: No, I was acquainted with him. But I didn't know him intimately. BERGE: Did he come over to UCSF or did you ever come over to Donner laboratory? KOHN: Rarely, rarely. Another topic I was interested in which raises an interesting question. We worked in the field of radiation genetics with the mouse. There have been only three or four or five laboratories, perhaps, who have donesignificant amounts of that kind of work in the United States. Now weworked with somethingcall the histocompatibility system. If you take a piece of skin and transplantit, from me to you, you will rejectit. Because we don't have the same genetic set up. On the other hand, if you take it from one identical twin to another, they will accept it because they have the same genetic set up. In the case of animals, say mice, we breed inbred strains, that is only brothers and sisters are mated and the special strain is thus established. And they for the most part accept skin transplanted from one another. But occasionally mutations will occur. Then when the skin is transplanted, that skin is rejected. So we know that there are numberof genes which control whatis called histocompatibility. In other words tissue compatibility. There may be as manyas, I don't know,forty such genesof which perhapsten or fifteen may be the more important ones. I should say a 12