SYLLABUS 



113 



stralglit at higher doses. The curvature is due to a stepwise kilHng 

 of the piiage (W'a'^son, iQsnl. The r<»*<. ^f inactivation i" i^.ilp- 

 pendent of oxygen present during irradiation (Dnprmann, per- 

 sonal communication) . 



The presence of long lived indirect agents is shown by the inac- 

 tivation of phage introduced into previously irradiated solutions. 

 The rate of inactivation is strongly influenced by such variables as 

 temperature and concentration of CI" ion (Watson, 1950). 



(b) Inactivation by Ultraviolet radiation (UV). Inactivation of 

 phages suspended in water or in a buffer solution is produced by light 

 of wave lengths of 3130A or shorter. An exceedingly slight inactivation 

 by hght of wave length 3600A or longer has been reported by Wahl and 

 Latarjet (1947). The action spectrum for inactivation is similar to the 

 absorption spectrum, and the quantimi yield at 2 53 7 A is of the order 

 of 10"* (Zelle and HoUaender, personal communication). 



The inactivation curves of the seven phages of the T group ap- 

 proach straight lines for high doses of UV (Luria and Latarjet, 1947); 

 at low doses the inactivation curves of phages T2, T4, T5, T6 show a 

 downward concavity, and those of phages Ti, T3, T7 show an upward 

 concavity (see Fig. 1). The origin of these curvatures is unknown 

 (Dulbecco, 1950). 



Inactivation by UV in dried condition has been obtained for phage 

 Ti (Fluke and Pollard, 1949). 



UV inactivation is dependent on dose only; it is independent of 

 intensity, fractionation of the dose, temperature during irradiation. 



(c) Inactivation by decay of P^^ incorporated in phage structure 

 (Hershey, personal communication). A particle of phage T2 is in- 

 activated on the average by one out of every 10 P^- transmutations 

 occurring in its structure. Only a small fraction of this inactivation 

 can be attributed to the beta particles emitted during transmutation. 



II. Glossary 



1 2 . To describe the standard methods of handling phages a certain 

 number of terms have been introduced which we now define. 



When working with one bacterial strain and one phage strain 

 conditions can be chosen so that most of the infected bacteria of a given 

 culture are infected with only one phage particle or with more than 

 one. The first case is called single infection, the second multiple in- 

 fection, and the ratio of adsorbed phage particles to bacteria in the 

 culture is named the multiplicity of infection. 



