At the time I gave my lecture, research was starting on a small DNA virus called polyoma, molecular weight only I think about 4 or 5 million. And it was nucleic acid, it couldn't be more than 2 million I think, which when injected into immunocompromised mice gave rise to a variety of tumors. And soon after, there was discovered a human virus - it was a monkey virus but it also multiplied in human cells - SV40, Simian virus 40. And so work began on both those systems. And sort of the hypothesis - and soon afterwards there was discovered in the nuclei of cells which were made cancerous by the virus there was a new antigen, it was called T-antigen or tumor antigen. And so that seemed to be a likely candidate for the protein that turned on DNA synthesis, so, well, this was - began to be studied pretty extensively by Renato Dulbecco at the Salk Institute. Renato and I had known each other since 1947 when he was a sort of senior post-doc [unclear] and Renato and I were in the same room. So we're long and good friends. And the culmination of Renato's work came in 1968-69 when the English post-doc's lab, Joseph Sambrook, did experiments which showed that the viral DNA after it got in the monkey cell became integrated into the host DNA. So it was very much like a lysogenic bacterial viruses, where the DNA instead of leading to a lydic system where the virus multiplies, becomes integrated into the bacterial DNA, and then upon certain signals which were at first obscure suddenly changed from being a [unclear] virus to suddenly leaving the chromosome and becoming a multiplying. So it seemed from Renato's work that at least my ideas that the viral DNA was carrying some information which made the cell cancer by inserting itself into the host DNA was right.