Quantitative studies with phage 7 obtained by specialized induction of strain 298 have been hampered by plaque counts showing marked random fluctuations with time and extreme variations in plaque size. The number of plaque-forming particles in phage 7 suspensions frequently fluctuated randomly by as much as a factor of 10 when stored for a week in a refrigerator. Many plaques were so small as to make accurate counting difficult. This appeared similar in many respects to the case of reversible inhibition by some part of the bacterial lysate reported by Sagik (1954) for phage T2. This paper gives results of a study which confirmed this initial suggestion and produced additional evidence on the nature of the phenomenon by the use of non-adsorbing lysogenic bacterial strains.

Several strains of were used: 297/32 (a small-colony variant of 297), 298/533 and 298/534 (large but distinct colony forms of 298), 298/531 (a small-colony form, also of 298) and 18.


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