It will, perhaps, surprise many readers, into whose ears a different version has been drummed for years, to learn that the first announcement of base-pairing in nucleic acids was made in an article, published early in 1950, which forms Chapter 1 of this book; the statement itself will be found on page 13. Those to whom it may sound unusually modest or restrained are asked to consider that at that time the new science of molecular biology did not yet exist.
should like to use this occasion to thank the several publishers for the permission to reprint these articles.
The last two chapters, Nos. 10 and 11, have not been pubHshed before and are of an entirely different kind, stepping forth, as they do, without the stately periwig of a list of references. They should be considered as a divertimento, though not without pas- sages in a minor key; specimens of a sort that rarely finds its way into a book dealing with scientific matters. Chapter 10 is a specimen of a recent lecture, as it was prepared for actual delivery, without undergoing the