CARCINOGENESIS BY IONIZING RADIATIONS 1179 



are 50,000 times lower than those that were found in people with bone 

 sarcoma induced by radium. 



Assuming an average radon content of 3 X 10~ 9 curie per liter of mine 

 air, Evans and Goodman (1940) estimated an hourly exposure of dry 

 lung to be equivalent to 0.17 erg per gram, and the corresponding daily 

 dose on the upper bronchial epithelium of the order of magnitude of 0.1 

 rep per day. Assuming seventeen years as an average tumor induction 

 time, the total dose would be 600 rep (estimated to equal 3000 rem; Evans, 

 see Brues, 1951). The dose effective in initiating the tumor would 

 obviously be much smaller. It is not known whether a particles are 

 more effective than X radiation for the same total dose. On the basis of 

 blood analyses Woldrich (1931) concluded that cancer of the bronchi is 

 caused by inhalation of radium emanation. 



Induction of lung tumors in mice requires either a comparatively 

 massive single dose or considerably higher chronic doses, as will be 

 detailed. In comparison to the mouse, man has a low incidence of spon- 

 taneous lung tumors; most tumors in mice are benign, while most of 

 those in man are malignant. In chronic exposures of man to radon in 

 the Schneeberg and Jachymov mines much smaller total doses are 

 involved than are necessary to induce lung tumors in mice. In breathing 

 air containing radon, the tissue dose of a radiation delivered to the 

 epithelium is, however, greatest in the larger bronchi where the primary 

 neoplasms are frequently located (Evans, see Brues, 1951). Radon gas 

 which emits a radiation becomes an atom of the solid radioactive sub- 

 stance RaA, decays into a series of radioactive elements of varying half 

 lives, which may adhere to the bronchial epithelium. Among other 

 factors which may contribute to the induction of these human tumors are 

 pneumoconiosis produced by the mine dust, and the cobalt and arsenic 

 content of the dust. Less likely is a hereditary susceptibility due to 

 inbreeding, mentioned by several investigators, or the carcinogenicity of 

 nonradioactive cobalt, chromium, and arsenic (see also Schinz and 

 Uehlinger, 1942; Hueper, personal communication). 



Abrahamson et al. (1950) described the development of bilateral 

 alveolar lung carcinoma in a patient who, sixteen years previously, had 

 received an intravenous injection of 75 cc of thorotrast. The liver and 

 spleen of the patient still contained much radioactivity at time of death. 

 The multifocal origin of the lung tumors in this patient is cited as evi- 

 dence for their induction by irradiation. 



Experimental Induction of Lung Tumors in Radioactive Mines. This has 

 been carried out either on a very small scale or without adequate con- 

 trols. Dohnert (1938) exposed mice in the Schneeberg mines at places 

 where the miners worked, but his uncontrolled experiments were incon- 

 clusive. Hereck (1939) reported on histologic changes in 110 mice 

 similarly exposed, of which five had adenomas of the lungs. Unfortu- 



