VIRUSES, CANCER, GENES, AND LIFE! — STANLEY 367 



However, human cancer is a fact and there is certainly something 

 within every human cancer cell that insures its reproduction whether 

 we call it a gene or a chromosomal fragment, and so long as human 

 viruses are so abundant we certainly have the possibility of trans- 

 duction. 



There are many examples of latent viruses that may remain hidden 

 for a lifetime or even for generations only to come to light as a result 

 of some treatment or change. Most human beings acquire the virus 

 of herpes simplex quite early in life and in many persons the evidence 

 for the persistence of this virus throughout their lifetime is quite 

 good. Traub has found that infection of a mouse colony with the 

 virus of lymphocytic choriomeningitis can result, with time, in an 

 inapparent infection of all animals. The virus is apparently trans- 

 mitted in utero and remains with the animal throughout its life ; hence 

 this virus persists throughout generation after generation of mice. In- 

 jection of such mice with sterile broth can revive the pathogenicity 

 of the virus and bring it into light. Certain potato viruses such as 

 potato X virus, also known as the healthy potato virus or the latent 

 mosaic of potato virus, can be passed from generation to generation 

 without causing an apparent disease. This virus is not present in 

 several varieties of potato grown in Europe, but it is thought to be 

 present in all, or almost all, potato plants grown in the United States. 

 Needless to say, it was only by virtue of the fact that potato plants 

 without this virus are known to exist and the fact that this virus 

 causes obvious disease symptoms when inoculated to certain other 

 plants that it was possible to establish the actual existence of this 

 virus. In the absence of this information this latent mosaic virus 

 would have to be regarded as a normal constituent of the potato plant. 



Since viruses can mutate and examples are known in which a virus 

 that never kills its host can mutate to form a new strain of virus that 

 always kills its host, it does not seem unreasonable to assume that an 

 innocuous latent virus might mutate to form a strain that causes 

 cancer. The great wealth of newly discovered viruses of man plus 

 our knowledge of the latent virus phenomenon provides ample justi- 

 fication to reexamine quite carefully the relationships between viruses 

 and human cancer. 



Another fact which may prove of the greatest importance in this 

 connection is that treatment of certain lysogenic strains of bacteria 

 with physical and chemical agents, such as X-rays, ultraviolet light, 

 nitrogen mustard, certain chemical-reducing agents or iron-chelating 

 agents, results, after a latent period, in the lysis of the bacterial cells 

 and the release of large amounts of bacterial virus particles. These 

 agents are called "inducers" and you may recognize some as carcino- 

 genic agents for man and animals. Nonlysogenic bacteria are un- 



