February 22, 1974
Dear Dr. Mirsky:
Upon consideration of the points made in your letter of January 29 I have decided to delete the offending reference.  I am glad you are writing an account of your own involvement in this important area, and I hope you will eventually send me a copy.
Yours sincerely,
Jack S. Cohen
Reproduction Research Branch
National Institute of Child Health and Human Development
Revised footnote 143.
Alfred Mirsky, also working at the Rockefeller Institute, has been mentioned as one of the chief questioners of DNA as the transforming substance by Chargaff (ref. 75), Hotchkiss (ref. 144b) and Stent (Molecular Genetics, Freeman, San Francisco, 1971, p. 180).
Mirsky's views at the time are most clearly expressed as; Avery and his colleagues have shown decisively by inactivation experiments that desoxyribose nucleic acid is an essential part of the transforming agent, and if there actually is no protein in their preparation, it would be obvious that the agent consists of nothing but nucleic acid.  This is a conclusion of the greatest interest in the study of the chemical basis of biological specificity, and it should therefore be scrutinized carefully. There can be little doubt in the mind of anyone who has prepared nucleic acid that traces of protein probably remain in even the best preparations. With the tests now available for detecting how much protein is present in a nucleic acid preparation, it is probable that as much as 1 or 2 per cent of protein could be present in a preparation of "pure,  protein-free" nucleic acid.  One of the most sensitive direct tests for protein is the Millon reaction,