22 MUTATIONS 



these two levels is the proportion of cells. This difference is 3 X 10"^. 

 The expectation for 7 X 10'^ and 2 X 10^ is 1.4 X 10 -^i so that the 

 cells are in excess by a factor of about 2. 



Figure 4 shows much the same situation. This is another individual. 

 With anti-A — this is purely fortuitous — he has the same non-A level 

 as the other one. There is a lot of variability. Most people actually 

 have a non-A level of 10^. 



Well, then, adding anti-B and B carrier, we sweep out a lot of re- 

 maining cells, and then, with Ulex, we sweep out still more of the 

 remaining cells. The same when anti-B is used first. In this case, the 

 non-B level is 2 X 10"^, and then, with anti-A, we can sweep out most 

 of the remaining ones and we come to the same level here. The little 

 jogs appearing from time to time in these curves represent times when 

 we got worried about activity in the supernatant that was not in cells, 

 because of lysis that goes on during the experiment. This requires a 

 special wash. We always suspect such activity after a certain number 

 of stages, and rightly so. We get rid of the label in solution by washing 

 the cell samples in a very large volume of saline before the final cen- 

 trifugation and Cr^^ counting, so that we are dealing only with activity 

 in cells and not in solution. 



Here, the expectation is 7 X lO"*', and what we observed was 4 X 10"^ 

 of cells. You have, in this case, an even greater excess of cells than 

 in the other experiment. 



The question of the identity of the cells that are not A, B, or 0, but 

 are left here after Ulex, is perfectly open. A possible explanation for 

 them is that they are Bombay cells, as Dr. Lederberg suggested; at 

 least they are not agglutinable by Ulex, and that is a characteristic of 

 Bombay cells. 



Lederberg: Are they erythrocytes? 



Atwood: Yes, they are probably erythrocytes, because they are 

 lyzable. That's all we know about them. 



Lederberg: What would that rule out? 



Atwood: It would rule out white cells, generally speaking. You lyse 

 in 2 per cent acetic and this would save the label in the white cells, 

 and release the label from red cells. The same proportion of the label 

 can be freed from sedimentability at the end of the experiment as at 

 the beginning. 



As to other particulates anywhere above this bottom level you would 

 have to assume they behave like red cells toward these agglutinins, so 

 I am not worried about them too much. 



Cotterman: I'm not sure how this question comes into the argument 



