FOREWORD 



A child said What is the grass? fetching it to me with full hands; 

 How could I answer the child ? 



Interest in the physics of living systems, which was so active 

 in the mid-eighteenth century when Mayer, Hehnholtz, and 

 Tyndall were leaders in contemporary thought, has passed 

 through a relatively low period. The twofold reason has been the 

 remarkable biochemical advance and the tremendous revolution 

 in physics which started at the turn of the century — just as 

 viruses were being discovered. These two fertile fields for re- 

 search have kept biologists busy applying chemical ideas, and 

 physicists busy reformulating the laws of nature. In the mean- 

 time students of viruses, using predominantly bacteriological 

 methods, have uncovered a whole new form of living systems — 

 ultimate parasites perhaps — which perform to a miracle the act 

 of self-reproduction. As these objects took form, as filterable, 

 stable, manageable preparations developed, physical studies on 

 them began to be made. And as these studies began, the revolu- 

 tion in physics also ran its course. By 1933, when Stanley 

 produced paracrystals of tobacco mosaic virus, the final form of 

 quantum mechanics had been produced by Heisenberg, Schrod- 

 inger. Born, and Dirac. The physical theories underlying these 

 chemical processes were complete by 1935. It is not surprising, 

 therefore, that physics began to be applied to viruses to an 

 increasing extent from that time on. 



Now the physicist who approaches virus study feels two 

 emotions. The first is the excitement of a challenge: viruses are 

 at least representative of one form of life, perhaps the simplest. 

 So far, except to insist that thermodynamics applies to life, 

 the physicist has refrained from describing it in his own terms, 

 and now a system comes into his thought where perhaps such a 

 description is possible. Even more, the physical description may 



