CARCINOGENESIS BY IONIZING RADIATIONS 1177 



The carcinogenicity of a or emitters can be tested conveniently by 

 direct introduction into the subcutaneous tissue. The tumors induced 

 arise either in the epidermis or in subjacent connective tissue. Andervont 

 and Shimkin (1940) induced subcutaneous tumors by injection of col- 

 loidal thorium dioxide and Lisco ct al. (1947) by plutonium and colloidal 

 yttrium phosphate. In the former experiment the effect of metallic 

 thorium has not been excluded. Lacassagne and Rudali (1942) caused 

 the regression of papillomas by irradiation in five rabbits, but in one 

 rabbit a new tumor, histologically a rhabdomyosarcoma, developed at 

 the site of the originally benign growth twenty-eight months after the 

 irradiation. A similar sequence of events has been observed in man. 



Beta radiations from P 3 ' 2 are highly carcinogenic to the skin when 

 applied directly. The energy absorption from P 32 is limited almost 

 entirely to the skin (Raper ct al, 1946, and Raper, 1947). In experiments 

 of Raper ct al, all rats receiving single doses of 4000-5000 rep developed 

 skin tumors (see also Henshaw et al, 1946, 1947) and the number of loci 

 of tumors arising in some rabbits exceeded fifty. The lethal dose of 

 external radiation varied with the size of the animal, being approxi- 

 mately 4500 rep for mice and 7000 for rats. 



LUNG 



Lung Tumors among Miners of Schneeberg and Jachymov. There is no 

 doubt that ionizing radiations will induce lung tumors in experimental 

 animals, but it is still controversial whether radiations emitted by radon, 

 either inhaled as radon-contaminated air or present in the expired air 

 from radium deposits in the body, will induce lung tumors in man. Many 

 complicating factors make an evaluation of the problem difficult (Lorenz, 

 1944). With the extension of mining activity of radioactive deposits 

 throughout the world, exposure to inhalation of radioactive dust and gases 

 will constitute an increasing hazard, and this problem will therefore be 

 fully reviewed. 



The main information on the induction of lung tumors in man comes 

 from the study of this disease in the miners of the uranium mines of 

 Schneeberg and Jachymov (Joachimsthal) . The history of a strange 

 disease called Bergkrankheit among the miners of Schneeberg goes back to 

 the sixteenth century (Sikl, 1950). However, not until 1879 was it 

 recognized (Haerting and Hesse) that this disease originated in the lungs 

 and that about 75 per cent of all deaths of the miners was due to a neo- 

 plasm diagnosed erroneously as lymphosarcoma. These findings were 

 confirmed by Arnstein (1913) who corrected the diagnosis to squamous- 

 cell carcinoma and attributed 40 per cent of all deaths of miners during 

 the period of 1875 to 1912 to this tumor. The incidence of pulmonary 

 tumors in miners of both Schneeberg and Jachymov was reviewed by 

 Peller in 1939, who gave the mortality statistics contained in the accom- 



