110 BACTERIOPHAGES 



the concentration of antibody perceptibly. Therefore, the 

 kinetics is that of a first-order reaction, represented by the equa- 

 tion: 



-dPidt = KP/D 



Integration gives the very useful result: 



23D 



K= -y- logio (Po/P) 



in which A' is the velocity constant with the dimension minute ~\ 

 D is the dilution of serum (100 for serum diluted 1/100, etc.), 

 / is the time in minutes, Pq is the phage assay at zero time, and 

 P is the phage assay at time t. 



Burnet found that the kinetics of neutralization of phage CI 6 

 agreed satisfactorily with this equation at serum concentrations 

 from V30 to ^/3o,ooo• Phage neutralization was logarithmic to 

 an inactivation of more than 99 per cent, but then the rate 

 slowed, the survivors appearing to be more resistant. Most of 

 the phages studied by Burnet behaved in this manner, including 

 a streptococcal phage and a staphylococcal phage as well as 

 various immunological types of enterophages. However, he 

 noted that the neutralization of coliphages in serological group 

 3 deviated markedly from a first-order reaction, and that a 

 relatively large proportion of the phage population was resist- 

 ant to inactivation by even high concentrations of antiserum. 

 Delbriick (1945b) found that the neutralization of T2 and T7 

 obeyed the equations above, but that neutralization of Tl did not. 

 The rate of inactivation of Tl decreased progressively throughout 

 the course of the reaction. Similar anomalous behavior has 

 been observed with phages related to T5 (Adams, 1952), with 

 the M phages of B. megaterium (Friedman and Cowles, 1953), 

 and with D20, a relative of Tl (Adams and Wade, 1955). 



The value of K, the velocity constant, is a characteristic of a 

 particular lot of serum and may vary from one rabbit to another 

 or from one bleeding to another from the same animal. The 

 K value is a convenient measure of the neutralizing potency of 



