Preface 



Experimental biology at the present time is approaching a particularly- 

 interesting stage. It is probably true to say that in recent years biochemical 

 concepts have dominated all general thinking on the fundamental problems 

 of biology. There has been an miinterrupted succession of important dis- 

 coveries and there is as yet no sign of any drying up of the flow of discovery. 

 It is orthodox to believe that the way is now open to a comprehensive 

 understanding of the basic living process in terms of biochemistry, with 

 perhaps only an inspired continuation of progress along present lines being 

 necessary. There are some, however, who are more impressed with the 

 moimtmg difficulties of applying the methodology of chemistry to the complex 

 macromolecules of living systems and their interactions than with the 

 inevitability of their being overcome. 



Clearly the crux of biological thought today is the applicability of chemical 

 and physical approaches to the typical macromolecules, protein and nucleic 

 acid, of living substance. In this context virology seems to occupy a key 

 position among the biological sciences. Viruses are the smallest biological 

 units which manifest all the essential characteristics of life and many are 

 now known to be built up only of nucleic acid and protein. With the 

 development of new biochemical techniques useful in attacking the problems 

 of macromolecular structure viruses have become the material 'par excellence 

 for fundamental study. The very great discovery that nucleic acid pre- 

 parations possessmg virus activity can be obtained from virus-infected tissues 

 and from pure viral nucleoprotems has focused attention on nucleic acid as 

 the key material in virus activity, in genetic activity, and in the synthesis of 

 proteins and of nucleic acids. It would appear, therefore, that nucleic acid 

 structures contain the codes for the fabrication of every individual of every 

 species. Since some viral nucleic acid preparations can be obtained quite 

 pure, chemically as well as genetically, in lots of hundreds of milligrams, 

 it is obvious that the viral nucleic acids offer an especially favorable and 

 perhaps unique possibility of breaking the code and of approaching the 

 synthesis of a replicatmg structure. These represent great challenges in 

 virology and are, of course, of the greatest importance to science and to 

 mankind. 



There have been many systematic compilations of knowledge on viruses 

 as agents of disease in man, in animals, or in plants. To our knowledge, 

 however, the present work is the first to be published in English in which a 

 systematic attempt is made to cover the significance of experimental work on 

 viruses for general problems within and on the borderlines of biochemistry, 

 biology, and biophysics. Since it would be impossible for one or two persons 



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