1 o6 BENZER ET AL. 



The inactivation of T5 and of the other phages can be prevented 

 by any one of a number of divalent cations at much lower concentra- 

 tion than the stabihzing concentration of sodium ion. Tests have shown 

 that all metal divalent cations have a protective effect for phage except 

 lead and mercury. The concentration which offers maximum protec- 

 tion is 10"^ M. Calcium shows a considerable protective effect at 

 10"* M. The change of stability with changing concentration of diva- 

 lent cation is very much less violent than in the case of sodium ion. 



The meaning of these effects of cations on stability is not well 

 understood. 



Studies have been made on the stability of phages at high pres- 

 sures (Foster et al., 1949). The results will not be detailed here. 



The inactivation rate of T2 has not been studied accurately, be- 

 cause the inactivation curves often show irregularities which are diffi- 

 cult to reproduce and therefore difficult to analyze. This behavior 

 might be due to clumping of phages in groups of two or more. 



The effect of hydrogen ion concentration on the rate of inactiva- 

 tion has been measured for T5 (Adams, 1949) and T7 (Kerby et al., 

 1949). Over the range from pH 5.5 to 7.5, the rate of inactivation 

 seems to be independent of hydrogen ion concentration, but below 5 

 and above 9, the rate of inactivation is greatly accelerated. 



The seven T phages are rapidly inactivated at gas-liquid inter- 

 faces (Adams, 1948). The smaller phages, Ti, T3, and T7, are in- 

 activated at a faster rate than the other phages. This inactivation is 

 a physical inactivation rather than a chemical one. The rate of in- 

 activation is not affected by varjdng the gas (nitrogen, oxygen, and 

 carbon dioxide) with which the phage suspension is shaken or bubbled. 

 The kinetics of this inactivation is also of the first order. This inacti- 

 vation may be prevented by the addition of small amounts of protein. 

 Of the various proteins studied, gelatin gives the best protective effect. 



7. Serology. 



Bacteriophages as antigens. — Bacteriophages are generally good 

 antigens. They exhibit a rigorous serological autonomy. 



(a) Antisera prepared against the bacterial hosts are inactive on 

 the bacteriophages. 



(b) Antiphage sera previously exhausted by the bacterial hosts 

 retain their full activity towards the bacteriophage with which they 

 have been prepared. 



