Cells which can grow as cancers behave as if they arose from normal ones by genetic transformation. The malignant change can be induced in mammalian cells by the deliberate application of carcinogenic chemicals, oncogenic viruses, and ionizing radiation. These are environmental factors to which we are all sometimes exposed. Since they lead to the same type of heritable alteration, ie, persistent, uncontrolled, and haphazard cell multiplication, it could be inferred that the genetic determinants, presumably the deoxyribonucleic acid had been affected thereby.
Direct and pertinent evidence that the genes of microbial forms and many viruses of DNA is abundantly available, but, surprisingly, this has not been demonstrated heretofore for mammalian cells in a convincing way. The arguments offered thus far have been based only on analogy.
A new line of evidence, currently under development at the Sloan-Kettering Institute for Cancer Research, arose from a comparison of the mode of growth