January 23, 1941

Dr. A. M. Pappenheimer, Jr.

Department of Bacteriology

University of Pennsylvania

Philadelphia, Pennsylvania

Dear Dr. Pappenheimer:

I am very sorry to have been so dilatory about replying to your letter. It was a surprise to me to see that two months had gone by since it reached me—the period has been so busy that I have not noticed how long I was delaying. I was very much interested to read your reprints and your manuscript with Dr. Petermann. I am returning the manuscript under separate cover.

Some of the assumptions in my paper on the structure of antibodies were made for the sake of simplicity. Thus I can not contend that antibodies are necessarily elongated with their active groups at the extreme ends. The evidence which you have obtained shows that this assumption is not always right. Also if the antibodies aggregate the effective valence may be increased, as you suggest. It is not indeed required that the valence of the primary antibody molecule be restricted to 2, but it seems likely to me that most antibodies have the valence 2 because the process of antibody manufacture becomes more complex as the valence increases.

My theory does not require that the active part of an antibody be less stable than other parts. It does, I think, require that the stability of antibodies analogous to different antigens be in general different.

The situation regarding antigen activity in relation to strength of groups is not at all clear. I am not sure that the argument which I presented is sound, and nearly every immunologist with whom I have talked has found fault with my conclusion.

It would be very interesting indeed to know through experiment whether your enzyme treated antitoxin has or has not a higher proline content than the original untreated antitoxin.

Drs. Dan Campbell and David Pressman and I have been carrying on some experiments during the last few months. We have obtained precipitates with various simple substances containing two or more atoxyl groups and antitoxyl serum, verifying Landsteiner and van der Scheer's results, and we have got evidence that our dye solutions are not colloidal by observing their dialysis through cellophane.

I hope that I shall be able to talk with you some time. I shall try to visit the University of Pennsylvania on some eastern trip, and I hope that whenever the opportunity presents itself you will make a visit to our Laboratories.

Sincerely yours,

Linus Pauling

LP:jr

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