- 32 high concentration of alpha activity in atherosclerotic plaques, which he has designated as arterial tumors, are subject tomydetailed comnents on earlier pages of his paper. The liver cancer sites in thorotrast patients agree well with the deposition of administered sizeable amounts of thorium oxide and the consequent tissue damage, as do the - bone tumor sites in radium dial workers agree well with the deposition of sizeable amounts of ingested bone-seeking alpha emitters and the consequent bone damage, "The difficulties of The 4th sentence of the paragraph states: _ producing lung cancer by external radiation has been pointed out by Warren end Gates(29756) Such experimental difficulties have more ‘to do with species and strains of animals, getting high enough radiation doses from external sources into the lungs or into what may be appropriate lung structures for the species and strain of animal, without severely damaging too much lung tissue in other ways or other tissues between the radiation source and the lung and thereby causing competing earlier causes of death than the tumors of interest, Some laboratories have been producing lung tumors in experimental means by radiation from external sources. There have also been reports of epidemiological studies showing increased incidence of lung tumors in human beings following irradiation from external sources. The author's statement should not be taken to mean that radiation from external sources cannot cause lung cancer. The 5th sentence of this paragraph states: "The absence of cancers in muscular tissue, except at sites of thorotrast injection or plutonium injection, also is relevant to this issue." The author does not develop further the relevance or the issue referred to, or