56 BACTERIOPHAGES 



acid and alkaline ends of this range. The first-order velocity 

 constants differed from one phage type to another, ranging from 

 0.05 to 1.2 per minute. The velocity constant calculated from 

 the data of Campbell-Renton is 0.06 per minute. 



Surface inactivation can be completely prevented by adding 

 enough protein to the diluent to saturate the gas-liquid interface 

 and prevent access of the virus to the surface. For this purpose 

 10 to 100 ixg. of gelatin per ml. of solution are adequate. Sur- 

 face inactivation must be considered whenever virus prepa- 

 rations are diluted in buffer solutions free of protein or peptones, 

 especially when surface-volume ratios become large. Similar 

 losses can be expected at solid-liquid interfaces, and call for 

 similar precautions. 



The effect of denaturation at liquid-liquid interfaces has not 

 been studied systematically. Garen (personal communication) 

 isolated DNA from phage T2 by shaking aqueous suspensions 

 with chloroform. Hotchin (1954), on the other hand, reported 

 no inactivation of phage K on shaking with isobutanol-chloro- 

 form mixtures; he used this method as a step in purification of 

 the phage. From what has been said above the effects should 

 depend very much on total concentration of phage and other 

 proteins. 



10. Heat Inactivation 



D'Herelle (1926) noted that several phages were inactivated 

 by heating at 75 ° C. for 30 minutes, whereas some survived and 

 some did not after heating at 70 ° C. Observations of this type 

 led to the notion of a qualitatively defined inactivation tempera- 

 ture, characteristic for each phage, analogous to the thermal 

 death point used to report the results of similar tests with bac- 

 teria. Such qualitative information sufficed for practical 

 purposes, and led to the use of heat treatment in lieu of filtration 

 to eliminate bacteria from phage preparations. 



Quantitative study of the effects of heating showed that phages 

 are inactivated in accordance with first-order kinetics. The 

 temperature coefficient of inactivation is very high, the Ar- 



