CARCINOGENESIS BY IONIZING RADIATIONS 1187 



ous earth, followed 6 days later by X irradiation. The first tumor 

 appeared six, the second thirteen months after irradiation. 



A third tumor similarly induced was atypical bat also of bony origin. 

 A fourth tumor was a periosteal sarcoma, the fifth a myxosarcoma, and 

 the sixth an intracanalicular epithelioma. Tumors were not encountered 

 in rabbits treated either with this bacillus or X radiation alone. The dose 

 of X radiation was smaller than that required to produce radiodermatitis 

 (600 r) and in three rabbits it even failed to cause epilation. 



The great variety of the histological types of the tumors (osseous, 

 periosteal, aponeurotic, loose connective tissue, muscular and ductal- 

 epithelial) are attributed to the preparatory intervention of the inflam- 

 matory process, raising the sensitivity of different cells to X radiation. 



Burrows et at. (1937) fully confirmed the work of Lacassagne. They 

 produced a focus of inflammation in the groin in each of twelve rabbits by 

 injections of kaolin and of finely powdered silica suspended in olive oil. 

 These foci were exposed to X radiation, each receiving a single dose of 

 600 r. Among nine rabbits thus treated and surviving for two years or 

 longer, tumors appeared in the irradiated tissues in six. In four of these 

 rabbits the tumors were sarcomas that had produced metastases. 



On the one hand, X radiation has been employed in the treatment of 

 inflammation; on the other hand, there are numerous observations indi- 

 cating that inflamed tissues are more readily rendered cancerous than 

 normal tissues. Most of these observations were made in the course of 

 therapeutic irradiation of tuberculous joints, and the bone tumors devel- 

 oped in the area of irradiation. The predisposing factor of inflammation 

 frequently present in the female genital tract has been blamed for cancers 

 in the vulva, cervix, and uterus (Bumm, 1923). 



A cocarcinogenic effect of methylcholanthrene and externally applied 

 j8 radiation from P 32 was reported by Hamilton and Passonneau (1949). 

 Each of these agents alone caused skin tumors in 13.3 per cent of the 

 mice and, when combined in the same doses, in 53.3 per cent. 



Mottram (1937) observed the cocarcinogenic effects of benzopyrene 

 and ionizing irradiations. Painting the skin of mice twice weekly with 

 3,4-benzopyrene for six weeks caused some reaction of the skin but no 

 tumors. However, with continued painting or additional application of 

 a single dose of /3 or y radiation, an appreciable number of tumors was 

 induced. Similar results were obtained by Mayneord and Parsons 

 (1937), who used X radiation in combination with benzopyrene or 

 dibenzanthracene. 



An enhancement of the leukemogenic action of methylcholanthrene by 

 X irradiation was described by Furth and Boon (1943). Destruction of 

 hemopoietic tissues by X irradiation is followed by regeneration, and 

 during this phase mitotic figures are seen in abundance in sections of 

 blood-forming organs. It seemed probable that, during this phase, the 



