IMMUNOLOGICAL METHODS IN THE STUDY OF VIRUSES 543 



better than others, and that when a "good" antiserum is obtained, it is 

 advisable to complete a whole experimental series with this reagent. All three 

 reagents, virus, antibody, and host cells, are intrinsically variable; the most 

 that can be hoped for is that a system can be found in which they can all be 

 controlled sufficiently to provide a model system on which the implications 

 of any theoretical hypothesis can be tested. 



The present tendency to use tissue culture methods for all virological 

 procedures for wliich suitable cell types are available makes it desirable that 

 Dulbecco's approach should be followed up for other virus-antibody systems. 

 Probably the most important aspect to be clarified is in regard to the various 

 teclmical manipulations involving dilution of one or both of the reagents in 

 the original reaction mixture. This is the point at which Fazekas de St. 

 Groth's and Dulbecco's interpretations seem to be most at variance. If the 

 reduction in plaque coimt is to become the standard method for the accurate 

 estimate of viral antibody, it is most imjjortant that technique should be 

 standardized to give the most generally meaningful result. This is perhaps 

 the main justification for a sophisticated mathematical analysis of the 

 process. 



4. Inhibition of Hemagglutination by Immune Serum 



Where, as with viruses of the influenza (myxovirus) group, hemagglutina- 

 tion is a function of the virus particles themselves, another interestmg mode] 

 system is available. This has not yet been studied as elaborately as it deserves. 



Hirst (1942) showed that neutraHzation by immmie serum could be con- 

 veniently measured by the extent of inhibition of hemagglutination and 

 showed that the end point corresponded to a constant serum-virus propor- 

 tion. In Melbourne, much incidental work on the nature of the reaction has 

 been carried out over the last fifteen years, but no general accoimt has been 

 published. 



The following findings, which are of general interest to the problem of the 

 nature of virus-antibody interaction, may be noted: 



(1) Provided time is allowed for very dilute reagents to reach equihbrium, 

 the law of constant proportions holds to a close approximation, i.e., if in the 

 conventional fashion the serum concentration is plotted against reduction in 

 virus titer, a straight line at 45 degrees is obtauied (Burnet and Boake, 1945). 



(2) The apparent titer of an immune serum depends on the nature of the 

 fowl cells used as indicator of hemagglutmation. Anderson et al. (1946) found 

 that cells from individual fowls could be placed in a sequence which was con- 

 sistent in three distuict properties. At one end were cells w^liich gave the 

 highest hemagglutinin titer with standard virus and relatively low values 

 for specific antiserum titers, and which did not show any inhibition by normal 



VOL. I — 36 



