SONIC AND OSMOTIC EFFECTS ON VIRUSES 181 



inger and Delbriick (Chapter 5), must be explained. Although a 

 collision of so large an object is a slow and gentle matter, never- 

 theless, there must be an absence of specific charges except at the 

 tail, or such attachment would hold the phage in the wrong posi- 

 tion. If the only charges are on the tail then they must (a) be 

 specific and (b) exert enough force to orient the whole phage as it 

 approaches the bacterium. For the second purpose, we can sup- 

 pose that force must extend over several hundred Angstrom 

 units, and this can only be due to unneutralized opposite charges. 

 An energy equal to that of thermal agitation cannot be provided 

 by single, opposite charges, if the local dielectric constant is 

 taken as 80, but needs 10 or more to be effective at 100 A. The 

 mutual repulsive force, if these are all on the virus in the con- 

 fined region of the tail, is so great that it might well interfere with 

 nucleic-acid-protein binding. So the charge must be primarily 

 on the bacterium. Now, for the first purpose, there must be a 

 specific, related configuration, otherwise nonspecific binding 

 would take place. We are thus led to the idea of three or four 

 singly charged groups, each well away from the others, on the 

 end of the tail of the virus. The charge specificity thus becomes a 

 property of the organization of whole protein molecules between 

 one another and not of the surface of each separate molecule. 

 A second important point is made by Hershey. It will be re- 

 called that both for TMV and SBMV there is good evidence that 

 surface antigens are relatively small, probably only a fraction 

 of a protein molecule. Bearing this in mind one can argue thus. 

 Since, (a) the sulfur antigens are capable of being left behind at 

 attachment, (6) they are the same in the progeny resulting from 

 the same attachment, and (c) they are different from any bac- 

 terial antigens, there must be a way in which the nucleic acid can 

 coerce a small, detailed rearrangement on many protein molecules 

 or their precursors inside the bacterium. In this way, new, iden- 

 tical antigen molecules are made in a few minutes. This inescap- 

 able fact throws a strong light on the thoroughness with which 

 bacterial metabolism must become virus metabolism after infec- 

 tion. One's respect for the power of a biologically intact nucleic- 

 acid structure rises to even higher levels. 



