132 THE PHYSICS OF VIRUSES 



(c). Virus inhibition is a logarithmic function of the poly- 

 peptide concentration, a fact which is apparent from Fig. 5.3. 



(d) . The percent infectivity remaining is a falling logarithmic 

 function of the chain length, or the number of lysine residues. 

 The longer the chain, the more the inhibition of infectivity, but 

 only logarithmically so. 



(e). No precipitation of the virus occurs with free lysine. 



They propose as an explanation that charged groups on the 

 virus can combine with charged groups on the polypeptide which 

 can then link to a second virus particle to cause aggregation. 

 Aggregation does not occur at low and high pH. The reversibility 

 of the process suggests that the binding is not extremely tight. 

 For this reason, the longer the polypeptide chain the more 

 charged bonds can be formed and the better the combination 

 and inhibition. 



In the electron microscope, the virus particles can be seen 

 to be thicker and less uniform of surface. It is of interest that 

 large aggregates can only form when the excess of polypeptide 

 is not too great. It will be seen shortly that this is very much 

 like the formation of preci})itate with specific antibody. 



These experiments offer a new technique in virus work. It 

 may well be that inhibition of infectivity is general for all 

 viruses, or specific to some. Inhibition of bacterial infectivity 

 does take place (Burger and Stahmann, 1951), so some fairly 

 general property of viruses, as, for example, the covering of 

 the surface specific charges needed for attachment, may be 

 involved. 



Virus Serology 



All kinds of viruses are excellent antigens. Plant viruses, in 

 particular, are so good that if an infected plant is used to give 

 infectious sap, and this is injected into a rabbit, the majority 

 of the antibodies formed are attributable to the virus. This is 

 partly related to the size of viruses, which are larger than more 

 usual protein molecules, but it is probably also related in some 

 way to the strong function a virus can play in a cell — even in a 



