GLOSSARY 441 



Lysogenization: Infection of a bacterium by phage to produce a lysogenic 

 clone or subclone of descendants. Lysogenization occurs some time after, 

 or some bacterial generations after, the initial infection. 



Maturation: The conversion of vegetative phage into mature, infective phage 

 particles. 



Mixed indicator: A mixture of two bacterial strains capable of distinguishing 

 between phages lysing one strain only, and phages lysing both, on agar 

 plates. 



Mixed infection: Multiple infection with each of two or more kinds of phage. 



Multiple infection: Multiplicity of infection appreciably greater than one, so 

 that most of the bacteria in a culture are infected with more than one phage 

 particle. 



Multiplicity of infection: Ratio of adsorbed phage particles to bacteria in a cul- 

 ture. 



Multiplicity reactivation: Production of viable phage progeny in multiple in- 

 fection with individually inviable phage particles. 



Mutant: A phage (or bacterium) showing one or more discrete heritable dif- 

 ferences from a standard type called wild. Mutations may be accumulated 

 by a succession of steps, defined by the methods of isolation, and may be 

 ascribed to one or more loci, as determined by recombination tests. 

 The useful mutations of phages alter host range or plaque type, though 

 other classes are known. Plaque-type mutants of temperate phages are 

 often virulent. 



One-step growth of phage: A single cycle of infection and lysis, nearly synchronous 

 in all the infected bacteria of the culture, usually achieved by the one-step 

 growth experiment (Chapter II). 



Phage: Bacteriophage. Used as a noun with a singular verb in this book the 

 word usually means phage species (singular). Used with a plural verb 

 it usually means phage particles. Used in the plural it usually means phage 

 species (plural). 



Phenotype: The properties of a phage particle considered independently of the 

 properties of its offspring, which are determined by the genotype. In 

 general, a population of phage particles may contain phenotypic and geno- 

 typic variants of similar properties, only the latter yielding mutant stocks 

 in which the variation is preserved. 



Photoreactivation: Production of viable phage progeny in illuminated bacteria 

 infected with otherwise inviable phage. 



Plate: A flat culture dish for nutrient agar; to prepare a culture in such a dish 

 for counting bacterial colonies or plaques. "To plate" usually means "to 

 titrate." 



Productive infection: Infection followed by phage production. 



Prophage: The form in which phages are perpetuated in lysogenic bacteria. 



