August 2, 1943

To: Dr. D. Pressman

From: Dr. L. Pauling

I believe that it would be worth while to have another experiment run with the hapten R'X' in order to see whether or not the predicted effect of a difference in the two kinds of haptens when one antiserum is present in excess can be detected. I suggest that you use the mixture anti-R serum and anti-X serum in the ration 93:7, corresponding to your 12.8:1 mixture. I suggest that three series of experiments with this ration be carried through, one with 10 x 10^-9 mols of R'X' antigen, one with 100 x 10^-9, and one with 1000 x 10^-9. Each of these should give approximately 60 micrograms of precipitated antibody. It will be necessary to go to considerably lower hapten concentration than you used before. I suggest that you start , or end, with an amount of hapten considerably less than the amount of antigen. The maximum amount of hapten should be about the same as in the experiments carried out. If it would not make too many tubes, perhaps two-fold dilutions should be used, although I think that three-fold dilutions might be satisfactory. If three-fold dilutions are used, four of the tubes should correspond to those analyses already made.

Do the numbers 10^-3 and so on down for the hapten given on the sheet you turned over to me represent grams or moles of hapten?

I should like you to calculate three more curves for Figure 2, corresponding to B' = 20, 15, and 5, with B'' = 30, 35, and 45. Also on Figure 3 I should like four more curves calculated, those for total antigen = 20 and 80, respectively.

Linus Pauling

LP:jr

CC to D. H. Campbell