58 BACTERIOPHAGES 



and Tegarden (1950). In both cases the value below 65° C. is 

 exceedingly low, 5,000 and 14,000 calories. These low values 

 are probably due to chemical inactivation of the phages by some 

 substance in the broth diluent, which becomes inappreciably slow 

 in comparison with thermal inactivation above 65 ° C. With 

 these two exceptions, all Arrhenius constants recorded for wet 

 phage are above 70,000 calories. 



The inactivation constants for dry phages listed in Table IV 

 are difficult to interpret because drying itself inactivates most 

 phages and subsequent heating may merely continue the drying 

 process. Phage Tl is exceptionally resistant to drying, however, 

 and the dried phage is notably resistant to heat. The low Ar- 

 rhenius constant in this instance may, therefore, reflect the ef- 

 fect of drying on thermal denaturation. These results suggest 

 further experiments, as discussed by the authors (Pollard and 

 Reaume, 1951). 



It is obvious that different determinations of the Arrhenius 

 constant for the same phage do not always agree. A signifi- 

 cant clue to these discrepancies is found in the paper of Foster, 

 Johnson, and Miller (1949). These authors failed to obtain a 

 first-order inactivation rate for phage T5 in broth. However, the 

 addition of 0.01 A^ MgClg to the broth resulted in typical first- 

 order curves with a velocity constant about half that found in the 

 absence of added magnesium salt. The addition of phosphate 

 accelerated the inactivation. Since broth is not a chemically 

 defined medium it is not likely to give reproducible results from 

 one lot to another. 



In chemically defined media the heat susceptibility of phages 

 depends very markedly on the chemical composition of the 

 medium. Nanavutty (1930) found a coliphage to be inactivated 

 10 times faster in saline than in broth. Burnet and McKie 

 (1930) found several phages to be far more susceptible to heat 

 inactivation in 0.1 N solutions of sodium or potassium salts than 

 in broth. The addition of magnesium or calcium salts made the 

 salt solutions equivalent to broth as far as phage stability was 

 concerned. Similar results were obtained by Gratia (1940). 



