358 i{ \i)i AiioN ni(ti.(»r.v 



stage of iiif(>(t ion from the shape and slope of the suppression curve. This 

 can he utiHzed to identify tiic stages at which a certain Ircatment stops 

 virus reprochu'tion. For example, on exposure of l)acteria infected with 

 phage T2 to a temperature of 45°C, the changes in ultraviolet sensitivity 

 lake place normally for the first 7 min, after which no further change 

 occurs, as though at this time a temp(M-ature-sensitive reaction entered tlie 

 picture (Beii/cer, 19o(), unpublished data). 



Although no "cure" for phage-infected bacteria has been ol)tained in 

 this work, an extension of these studies to other viruses might produce 

 results of some therapeutic value in \ irus infection. Even if the cells 

 already infected could not be saved by radiation, suppression of their 

 ability to liberate virus might prevent the spreading of infection. The 

 value of such a procedure would depend on the relative sensitivities of the 

 infected cells and of the normal tissues. Experiments on rabbit papil- 

 loma have shown that growth of the papillomas can be suppressed by 

 doses of X rays much smaller than those necessary to inactivate the \^irus 

 in vitro (Syverton, Berry, and Warren, 1941; Syverton, Harvey et al., 

 1941). Actually, virus can be recovered in undiminished amounts from 

 the irradiated papillomas (Friedewald and Anderson, 1943). Here the 

 radiation probably acts on the host cell, rather than directly on the intra- 

 cellular virus, in the same way as therapeutic doses of X rays affect 

 bacterial infections bj' acting on the tissues of the host. 



5-2. RADIATION AND LATENT VIRUSES 



An interesting possibility is that of affecting, by means of radiation, 

 viruses which may be present in the latent state, i.e., viruses which do not 

 manifest themselves and which behave up to a certain point like normal 

 cell components. The distinction between latent viruses and cell com- 

 ponents is not always easy with the available knowledge and in some cases 

 may actually be academic. Any self-reproducing element of the proto- 

 plasm of a cell might conceivably become a virus if by some evolutionary 

 accident it should ac(iuire the ability to enter other cells and there repro- 

 duce its own kind. Such an origin of viruses has been suggested, but the 

 question will remain academic until more definite knowledge is obtained in 

 regard to the occurrence and properties of self-reproducing units (other 

 than the nuclear genes) in most types of cells. Should such units be more 

 widespread than they appear to be, their origin in the process of cell evolu- 

 tion would still be unknown. It is known that a virus may enter a cell 

 and reproduce while the cell goes through several cell generations, often 

 without causing recognizable cell disturi)ances. Such a virus behaves at 

 least for some time as a cell component. This type of symbiosis often 

 prolongs itself for many cell generations, and in multicellular organisms 

 some viruses are transmitted through the gametes from generation to 

 generation. The recognition of the virus depends then only on indirect 



