Letter from Charles A. Doan, Ohio State University to Michael Heidelberger

In this letter, Doan proposed experiments with dye solutions of egg albumin, a major plasma protein, in an attempt to make immune reactions visible and to understand their mechanism better. Heidelberger had pioneered the use of dye solutions in immunochemistry--a red dye bound to albumin or to streptococcus antigen--and had supplied such dyes to Florence R. Sabin at the Rockefeller Institute for her research on tuberculosis bacteria chemistry and the immune responses to these bacteria.