his “mouth fell open”: Watson 1980, p. 98.

Jerry Donohue came to the rescue: At the time, there were uncertainties concerning the precise location of the hydrogen atoms in the bases. (There were different so-called tautomeric forms.) Donohue was an expert on the subject, eventually publishing important works in 1952 and 1955. His contribution to the successful DNA model was crucial.

From the symmetry of the crystalline DNA: In crystallography, symmetry (with respect to transformations such as rotation and reflection) is used to characterize the crystals. From the information in the report, Crick was able to deduce that the crystalline form of DNA could be described by what crystallographers call the “monoclinic C2” space group. This, in turn, implied that the chains were antiparallel. In an interview with Robert Olby, Crick admitted, “I don’t think I would have thought of running them in the other direction” (Olby 1974, p. 404).

“I enclose a draft of our letter”: Gann and Witkowski 2010.

“If Rosy wants to see Pauling”: Letter of Wilkins to Crick, probably on March 23. Gann and Witkowski 2010.