RADIATION AND VIRUSES 359 



tests, either the inoculation of tissue extracts in a virus-susceptible host or 

 the search for antivirus antibody in the latently infected organisms. The 

 distinction between virus and cell component is thus (luite difficult. The 

 information relevant to this area of biology caiuiot be discussed here. In 

 connection with the possil)ility of affecting latent viruses or self-repro- 

 ducing cell components within cells as a means of analyzing the relation 

 between these entities and the cell as a whole, some radiation results 

 are pertinent. 



5-2a. Irradiation of Lysogenic Bacteria. Lysogenic bacteria carry one 

 or more bacteriophages in a latent form without recognizable manifes- 

 tations. In these bacteria the phage is apparently present as immature 

 virus or "prophage." Occasionally a lysogenic cell is lysed and liberates 

 a cluster of mature phage particles, whose presence can be recognized if a 

 susceptible strain of bacteria that responds to phage infection by lysis is 

 available (Lwoff and Gutmann, 1950) . In the course of attempts to define 

 the conditions that lead to the occasional maturation of virus in the lyso- 

 genic bacteria, it has been discovered (Lwoff et al., 1950) that ultraviolet 

 irradiation produces in some lysogenic strains a massive lysis accompanied 

 by liberation of mature phage. This suggests that something in the lyso- 

 genic bacteria prevents the maturation of prophage into bacteriophage, 

 thus preserving the symbiotic relation, and that ultraviolet, by removing 

 the inhibition, releases the maturation process. 



5-2b. Irradiation and Cytoplasmic Factors. Another pertinent obser- 

 vation concerns the destruction by radiation of the cytoplasmic factor 

 "kappa" in Paramecium aurelia. Some strains of this organism produce 

 a poison (paramecin) which is lethal for individuals of other strains. The 

 production of the poison is always associated with the presence in the 

 cytoplasm of the killer animals of peculiar Feulgen-positive particles, 0.3- 

 0.8 M in size, which are the material carriers of a genetically recognizable 

 self -reproducing mutable factor (kappa). The continuous production of 

 kappa depends both on the presence of preexistent kappa and on the 

 proper genetic background. Kappa has been transmitted from one indi- 

 vidual to another by "infection " with cell extracts, thus resembling a virus 

 or a rickettsia (Sonneborn, 1949). 



X rays (Freer, 1950), as well as ultraviolet (Sonneborn, personal com- 

 munication) and nitrogen mustards (Geckler, 1949), eliminate the killer 

 factor from the protoplasm at a rate that suggests a one-hit inactivation 

 process with an inactivation dose of approximately 4000 r. This dose is 

 comparable to the doses required for sterilization of bacteria which are 

 somewhat larger in size than the kappa particles. This result suggests 

 interesting applications of radiation analysis to the study of cytoplasmic 

 inheritance and encourages speculation on the possible use of selective 

 effects of radiation on cytoplasmic elements in modifying de\-elopment 

 and differentiation (which have been suggested to be controlled by cyto- 



