114 BACTERIOPHAGES 



resistant survivors of the action of Vioo serum were inactivated 

 by Vio serum at the same rate as untreated phage particles; 

 however, the description of this experiment leaves much to be 

 desired. Attempts to correlate resistance to antiserum with 

 other properties such as heat resistance, abihty to adsorb to 

 host cells, age of phage stock, and plating efficiency on different 

 bacterial hosts were unsuccessful. 



Delbriick (1945b), dealing with the anomalous neutralization 

 behavior of Tl, suggested that the inhomogeneity might be 

 inherent in the virus population or, more likely, that it might 

 develop during the course of the reaction as a result of attach- 

 ment of antibody at noncritical sites on the phage. Although 

 many samples of anti-Tl serum are like that described by Del- 

 briick in failing to follow first-order kinetics, Hershey (personal 

 communication) found that anti-Ti sera from two rabbits gave 

 excellent first-order inactivation curves. Similarly, Fodor and 

 Adams (1955) found only one antiserum, of some dozen pre- 

 pared against various strains of the T5 serological group, which 

 gave good first-order neutralization curves. It is not clear, 

 therefore, whether the observed neutralization anomalies 

 reflect an inherent heterogeneity of phage preparations, to 

 which not all rabbits respond, or a heterogeneity which is ac- 

 quired during interaction with certain samples of antiserum. 

 Nor is it clear that the responsible serum factor is necessarily 

 specific antibody. According to Hershey and Bronfenbrenner 

 (1952) anomalous neutralization behavior may be an uncon- 

 trolled effect of complement. Recent studies (Van Vunakis, 

 Barlow, and Levine, 1956) show that serum properdin, together 

 with complement, have nonspecific effects which could confuse 

 the study of specific neutralization. Unfortunately, nonspecific 

 serum efl?"ects have not received explicit attention in most studies 

 of anomalous neutralization behavior. 



11. Host Dependence of Serum-Survivor Assay 



It has been known for many years (d'Herelle, 1926) that difl^er- 

 ent assay hosts may give diflfcrent estimates of the fraction of 



