174 BACTERIOPHAGES 



results of such an experiment using the same culture of E. coli 

 infected with phage T3 that was used for the other two curves in 

 the figure. The base line for the cyanide-T6 lysis curve is very 

 low, corresponding to less than one per cent of the infected bac- 

 teria, showing that this method of lysis is very efficient. Other- 

 wise the two methods of premature lysis yield remarkably 

 similar curves. This suggests that either method accurately 

 measures the intracellular content of infective phage particles at 

 the time of sampling. 



Two important conclusions about the multiplication of phage 

 T3 may be drawn from these results: (7) during the first half of 

 the latent period there are no mature phage particles inside the 

 infected cell (this interval is called the "eclipse period"), and 

 (2) during the second half of the latent period the number of 

 mature phage particles increases rapidly, reaching an average of 

 about 50 per infected bacterium at the tim.e when spontaneous 

 lysis begins. 



Doermann (1948b, 1952) also studied the growth of phage T4 

 by premature lysis, and many other phages have been studied 

 since with similar results. Doermann also noted that cyanide or 

 5-methyltryptophan alone could cause premature lysis when 

 added after the end of the eclipse period. Other lysing agents 

 have since been used, notably proflavine (Foster, 1948; De- 

 Mars, 1955), dinitrophenol (Heagy, 1950), shaking with glass 

 beads (Joklik, 1952), decompression under nitrous oxide (Fraser, 

 1951b; Levinthal and Fisher, 1952), glycine at high concentra- 

 tions (Kay, 1952; DeMars, 1955), chloroform (Sechaud and 

 Kellenberger, 1956), and chloramphenicol (Tomizawa and 

 Sunakawa, 1956) (see also Chapter XV). 



In all of these methods some means must be used to prevent 

 loss of the liberated phage by adsorption to bacterial debris. 

 One may use dilution as in the usual one-step growth experiment, 

 a culture medium unfavorable to adsorption, an inhibitor of 

 adsorption (French, Graham, Lesley, and Van Rooyen, 1952), 

 or addition of a large excess of homologous irradiated phage 

 (Maal0e and Watson, 1951). In the latter case the irradiated 



