Preface 



Few recent advances have, for better or for worse, had such an 

 impact on biological thinking as the discovery of base-pairing in 

 nucleic acids. These complementariness principles do not only 

 underlie current ideas on the structure of the nucleic acids, but 

 they form the foundation of all speculations, more or less well- 

 founded, on their physical properties (denaturation, hypochromic- 

 ity, etc.), on the transfer of biological information from deoxy- 

 ribonucleic acid to ribonucleic acid, and on the role of the latter 

 in directing the synthesis of specific proteins. They form the basis 

 of present explanations of the manner in which the amino acids 

 are activated before being assembled to make a protein; they are 

 being invoked incessantly in attempts to unravel the nucleotide 

 code which is thought to be responsible for specifying the amino 

 acid sequence of proteins. 



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. 



Chapters 2 to 9 are also drawn from essays published pre- 

 viously at different times and at different places, some not easily 

 accessible. They are all reprinted here without change, with the 

 exception of Chapter 9 which underwent extensive revision. 

 Place and year of publication are indicated in each case; and I 



