200 THE PHYSICS OF VIRUSES 



is taking i)lace rapidly, as in all active living systems, and the 

 nature of tlie process is of deep interest. In many of the systems 

 with which physics and chemistry have to deal, the transfer of 

 energy requires the generation of a certain amount of random 

 thermal motion and its transfer partly to different random mo- 

 tion (at a lower temperature) and to definite linear motion. This 

 is inherently impossible in biological systems which are at one 

 uniform temperature. Schrodinger (1945) has pointed out the 

 general mechanism by which this biological energy transfer takes 

 place, and Delbriick (1946) has shown very clearly how it oper- 

 ates in one or two special cases. 



Energy turnover takes place by means of atomic rearrange- 

 ments. These do not take part in a statistical system, they have 

 no "temperature," but rather involve a direct and very efficient 

 method of moving energy from one form to another. Thus a 

 loosely bound phosphate group can become a tightly bound 

 group with the release of 2 or 3 ev of energy. However, the re- 

 leased energy does not have to cause random thermal agitation, 

 but can produce the necessary excitation to break a bond and 

 permit a new configuration which carries a high percentage of the 

 original released energy. Almost certainly the function of en- 

 zymes is to hold systems in place so that such energy transfer can 

 take place through the enzyme molecule and effect the required 

 change. The energy shift is rapid and at high efficiency. 



The host cell has thus an equipment comprising specialized 

 enzyme molecules, small co-factor molecules which can form 

 temporary structural unions, as well as a basic medium of small 

 molecules and ions. A part of the necessary behavior of the cell 

 is the assembly of nucleic acid and protein structural units. These 

 are formed from the simple molecules of the medium supplying 

 the host, either directly after assimilation through a membrane 

 as in the case of a bacterium, or through the more complex proc- 

 esses of an animal or plant. These units evidently carry with 

 them a specific character, probably imposed by the general na- 

 ture of the enzymatic protein, which is a simple repetition of a 

 rather limited number of amino-acid side chains in the case of a 

 small polypeptide precursor, or an order to the nucleosides in the 



