Letter from Oswald T. Avery to Michael Heidelberger

In this letter Heidelberger's former mentor and collaborator Oswald Avery, affectionately called "Fess" by his colleagues, congratulated him on the development of his quantitative theory of the precipitin reaction. A break-through in immunology, the theory established the multivalence of antigens and antibodies, or the ability of each to form chemical bonds with two or (in the case of most antigens) more molecules of the other. "I rejoice to see the mysteries of immunological phenomena yielding beautifully to the laws of classical chemistry," Avery wrote.