368 ANNUAL REPORT SMITHSONIAN INSTITUTION, 195 7 



affected by these "inducers" in so far as the production of a bacterial 

 virus is concerned. Is it possible that this activation of a prophage by 

 certain chemical or physical agents with development into a fully 

 infectious bacterial virus and the consequent destruction of the bac- 

 terial cells provides a biological example of a process which occurs in 

 man? I believe that this activation of prophage as well as the phe- 

 nomenon of transduction by free deoxyribonucleic acid in the pneu- 

 mococcus and by bacterial viruses in Salmonella is pertinent to the 

 human cancer problem, especially so in view of the recent discovery of 

 dozens upon dozens of new viruses of man. Certainly the experi- 

 mental evidence now available is consistent with the idea that viruses, 

 as we know them today, could be the etiological agents of most, if not 

 all cancer, including cancer in man. I have been urging the accept- 

 ance of this idea as a working hypothesis because it will result in the 

 doing of experiments that might otherwise be left undone, experi- 

 ments that could result in the solving of the cancer problem. Needless 

 to say, what we do in the way of experimentation depends in large 

 measure upon what we think and I am sure the time has come when 

 we should change our thinking with respect to the nature of cancer. 



I hope that by this time it is obvious that viruses, cancer, genes, and 

 life are tied together by a whole series of relationships, that viruses 

 can act as genes and genes as viruses under certain circumstances, that 

 viruses can cause cancer and that viruses are structures at the twilight 

 zone of life partaking both of living and of molecular properties. Let 

 us now see whether there is a common thread of understanding per- 

 meating all these relationships. We know that viruses have been 

 thought to be at least as complex as a nucleoprotein, but we also know 

 that the transforming agent of the pneumococcus has been found to 

 be a deoxyribonucleic acid and there is presumptive evidence that the 

 genetic stuff of the bacterial viruses is also deoxyribonucleic acid. 

 However, until recently no gene or chromosome or any of the ordinary 

 viruses had been isolated as such in the form of nucleic acid ; hence the 

 "stuff of life," as well as the viruses, has been considered to be nucleo- 

 protein in nature with considerable doubt as to whether the protein 

 or the nucleic acid or the combination of the two was really the bio- 

 logically active structure. 



A recent very important discovery made in our laboratory by 

 Doctor Fraenkel-Conrat has changed the situation considerably and 

 now makes it seem certain that nucleic acid is the all-important 

 structure. It was reported by Fraenkel-Conrat and also shortly there- 

 after by Gierer and Schramm in Germany that special treatment 

 of tobacco mosaic virus yielded a nucleic acid preparation possessing 

 virus activity. It would now appear necessary to recognize that a 

 nucleic acid structure of around 300,000 molecular weight can 



