1094 RADIATION BIOLOGY 



can be brought about by certain chemical agents. This is true, for 

 instance, for the hematopoietic organs, intestine, and testis after injection 

 of appropriate amounts of the nitrogen or sulfur mustard gases. These 

 and many other substances are also potent mutagenic agents. Moreover, 

 benzol has for many years been known to deplete the blood-forming 

 tissues in much the same fashion as X rays. 



Although there is nothing known that is specific for radiation effects, 

 it is often possible within certain dose ranges to diagnose radiation 

 damage. Thus, "The combination of two or more of the nonspecific 

 characteristics of radiation is strongly presumptive evidence that the 

 injury is in fact the result of radiation. Thus the combination of giant 

 and irregular nuclei, hyaline connective tissue, and thick-walled hyalin- 

 ized blood vessels would be difficult to explain on any other basis than 

 that of a late response to irradiation " (Shields Warren, 1944). However, 

 the acute changes due to nitrogen mustard and irradiation are identical. 



For detailed consideration of the several thousand papers dealing with 

 changes from irradiation from external and certain internal sources, the 

 reader is referred to a number of extensive reviews (W. Bloom, 1948a; 

 Colwell, 1935; Desjardins, 1924, 1926, 1928, 1931; Dunlap, 1948; Ellinger, 

 1941; Giese, 1947; Lacassagne and Gricouroff, 1941; Packard, 1931; 

 Regaud and Lacassagne, 1927 ; Shields Warren, 1942, 1943, 1944; Stafford 

 L. Warren, 1936). Here we can only attempt to summarize the more 

 important of these changes. Whenever possible, the data emphasized 

 will be from experiments on laboratory animals, where control of dosage, 

 intervals, and a large number of subjects under identical conditions is 

 possible. In most of the organ systems the effects of moderate single 

 doses of external irradiation will be described first, followed by the changes 

 resulting from smaller or larger doses, then those after repeated small 

 doses, and finally the effects of internal irradiation. 



VISIBLE CHANGES IN CELLS 



The first changes of irradiation are usually manifest as nuclear changes, 

 often those involving the mitotic process. Most of the evidence since 

 1903 (Perthes, 1903) indicates that the nucleus is more sensitive to 

 irradiation than the cytoplasm. This view has received direct experi- 

 mental confirmation in the comparison of the effects of irradiation of 

 cytoplasm plus nucleus with cytoplasm alone in fern spores (Zirkle, 1932). 

 Similar conclusions were reached on Arbacia eggs (Henshaw, 1938). 

 However, the opposing view that nuclear changes are secondary to 

 changes in the cytoplasm has been strongly maintained (Duryee, 1949; 

 see also Chap. 10 by Giles and Chap. 11 by Carlson). 



Cell Membrane. There have been several reports that the cell mem- 

 brane is damaged by irradiation. The most convincing instance, in the 



