1130 RADIATION BIOLOGY 



The process may still be continuing six months after irradiation. With 

 subepidermicidal doses the changes are mild although some fibrosis is left. 

 Epidermicidal doses produce extensive sclerosis, often with bone forma- 

 tion. Such doses are often lethal. The time-intensity factor is impor- 

 tant, since with fractionation and protracted dosing the changes are less. 

 As the pulmonary vessels were found to react strongly to pharmaco- 

 dynamic drugs in these animals, Engelstad does not believe that the 

 primary action is on the blood vessels. Cartilage in the conducting 

 passages is radioresistant to these doses. The bronchial epithelium shows 

 great abnormalities, and often becomes stratified and even cornified. 

 The pleura is resistant. 



These findings have been amplified by Shields Warren and Gates (1940) 

 in studies on a variety of species, including man. They describe the 

 first change as swelling of cells lining the alveoli and atria. These cells 

 may not become larger than macrophages although they may show some 

 anaplasia, especially in man. In man, but only infrequently in animals, 

 a hyaline membrane is prominent in influenzal and other pneumonic 

 lesions, including irritant gas poisoning. After irradiation this membrane 

 is usually seen close to the alveolar wall in alveoli which are distended 

 and usually free of exudate. The membrane is not fibrin ; it is probably 

 an increased and condensed amorphous ground substance. Later, some 

 splitting of elastic fibers occurs. Bronchial epithelium, in contrast to 

 that of alveoli, is relatively stable. There may be some increase in 

 mucous cells. The columnar cells become cuboidal, often with loss of 

 cilia, but do not become stratified columnar. Bronchiolar epithelium is 

 probably as sensitive as that of the alveolar wall. The increase in size 

 and fusion of epithelial cells noted in animals do not occur in man. These 

 investigators conclude: "Epithelial anaplasia, alveolar and bronchial, 

 ruptured and reduplicated elastica, and hyaline membrane lining alveoli, 

 combined, we have seen in no other disease process. The first two of this 

 triad are seen in irradiated skin. The third occurs rarely in a variety of 

 inflammatory conditions in the lung ..." (Shields Warren and Gates, 



1940). 



Both post-mortem and experimental data have proved that the 

 roentgenologic pictures and clinical symptoms usually represent transi- 

 tory changes, which are generally harmless. In the late reaction, thicken- 

 ing of alveolar walls, patchy atelectasis, and vascular change are out- 

 standing, but the more acute change may be present also. Fibrosis, 

 though often present, has not been established as a radiation effect inde- 

 pendent of intercurrent infection. There is some reason for thinking 

 that most pleural fibrosis is a result of infection rather than injury from 

 irradiation; the mesothelium is radioresistant. There is some clinical 

 and experimental evidence that inflammation of the lung may render its 

 tissues more sensitive to radiation (Shields Warren and Gates, 1940). 



