1120 



RADIATION BIOLOGY 



physical injuries; it forms blisters readily, in contrast to the skins of prac- 

 tically all other animals, which do not. 



The gross changes in the skin extend from erythema and epilation 

 (and, in some cases, pigmentation in human skin), which result from 

 exposure to 500 to 800 r, to more marked changes with higher dosages, 



which result in thin, fragile, 

 regenerating epidermis, sclerosis 

 of the derma, and necrosis and 

 ulceration. The extent of the 

 injury to the skin varies with the 

 amount of radiation absorbed 

 (the effect is also greater per 

 roentgen of soft X rays) , with the 

 animal species, with different 

 individuals of the same species, 

 and even with different areas on 

 the body of the same individual. 

 This last difference is important 

 when using erythema as a criterion 

 of dosage. 



Epithelium. The first change 

 to be seen after irradiation with 

 doses up to several hundred 

 roentgens is a temporary cessa- 

 tion of mitosis in the lower layers 

 of the epithelium. It has even 

 been claimed that with 35 r the 

 mitoses in the epidermis of the 

 mouse ear are markedly decreased 

 (Knowlton and Hempelmann, 

 1949). Two to 6 or 8 days after 

 300 r in human skin, there are 

 clumped chromosomes and some 

 atypical mitoses and the debris of 

 mitoses. No more dividing cells 

 are found until about the twen- 

 tieth day. Usually there are only 



Fig. 17-7. Section of base of crypt from a 

 duodenum of art exposed 28 hours pre- 

 viously to 600 r of 200-kv X rays, total-body 

 irradiation. There is still much debris 

 among the cells in the crypt epithelium and 

 several mitoses indicative of beginning 

 regeneration. There are also enormously 

 swollen cells considerably larger than the 

 normal cells. 1270X. (After Pierce, 1948.) 

 Drawn by Esther Bohlman. 



a few binucleate cells. From 20 

 to 40 days there is a variable amount of nuclear polymorphism, with 

 large and small cells and occasional binucleate cells (Miescher, 1938). 

 The mitoses now are of normal appearance and the epidermis is not 

 thickened. 



Exposure of human skin to 600 to 1200 r produces some degeneration of 

 cells of the germinative layer. With these larger doses the number of 



