FIRST EDITION. 8vo. (8.6 x 5.7 inches). Illustrated with 19 half-tone photographic plates, including six pages reproducing Watson's letter to Max Delbruck, telling of the Double Helix, and 11 diagrams within the text. A very bright, clean copy. Original dustwrapper with one small chip and a couple of small closed tears, otherwise a better than very good example. Overall a very good copy.