January 21, 1953

Dr. Linus Pauling

California Institute of Technology

Gates and Crellin Laboratories of Chemistry

Pasadena 4, Calif.

Dear Linus:

In reply to your letter of January 15, the paper "The Electron Microscopy of Sodium Desoxyribonucleate" by H. Kahler and B. J. Lloyd, Jr. is in press in Biochimica and Biophysica Acta. Enclosed is an abstract presented before the Electron Microscope Society.

In this paper we conclude that the diameter of nucleic is 15 + 5 Ǻ. Most of our measurements were actually within the range of 15 + 2 Ǻ, but there is some uncertainty about the exact place where the shadow ends. An arbitrary decision has to be made in making the measurement, and since this decision made lead to a systematic error of a couple Ǻ we leaned backwards and simply put a round figure 5 Ǻ as the overall error. In any event, I would be surprised if the diameter is greater than 20 Ǻ. Our photographs have one important advantage over those of Williams in that the fibers tend to lie in a flatter position on the substrate film, whereas in his technique most of the fibers are partly off the film due to the freezing process. However, it was very satisfying to find that we both got the same value in completely independent determinations.

I am very much interested in your paper and should like to receive a reprint as soon as possible.

With best wishes.

Sincerely yours,

Herbert Kahler

Enclosure