- 33 indicate the types of cancers to which he is referring. This statement should not be taken to mean that other radioactive isotopes injected into similar regions, or irradiation from external sources in one or another mode, cannot cause similar cancers. In the 6th sentence of this paregraph, perhaps the author is giving the purpose for his previous two sentences. He states: "All of these observations reinforce the possibility that one or more of the chromosomal changes which characterize a malignant cell must be brought about by alpha interactions and not by low intensity x-rays or y-rays." Although this sentence has enigmatic characteristics, a mixture of confusing ut qualifications, % will take it literally and state that it is not well founded and is neglectful of the evidence for x-ray and y-ray induction of mutations, chromosomal aberrations, and cancer. Nor does it address the possibility that malignancy may result from completely different mechanisms than those postulated by the author, or through several different mechanisms, one of which may be chromosomal abnormalities resulting from radiation, Page 15, lines 3-13 - "It is also observed that the relative Significance of chemical agents, viruses and radiation in the incidence of human cancer is not known. Details of the mechanisms of cancer induction by chemical agents and viruses also are poorly understood. And the proposed chemical carcinogens in cigarette smoke and in polluted urban environments have not been demonstrated to be carcinogenic at the low cohcentrations involved. For all of these reasons it is deemed likely that radiation, and alpha radiation in particular, may be the principal agent of human cancer. [In view of such a possibility, it is very disturbing to note that the U.S. National Cancer Institute, now spending about one-half billion dollars per year on cancer research, has completely neglected the field of radiation induced cancer research."