HISTOLOGICAL CHANGES AFTER IRRADIATION 1097 



have been described as a primary effect of radiation (Alberti and Politzer, 

 1923) . Some of these dumpings may be pseudo-amitotic. Then, follow- 

 ing the period of inhibition of mitosis, the secondary effect appears, 

 manifested by karyorrhexis in cells which were resting at the time of 

 irradiation. In animals given a second irradiation 10 or 15 days after 

 the first, the primary effects were complicated by secondary effects from 

 the first irradiation. 



Many of the cells which are in a resting state at the time of irradiation, 

 as well as some that are in mitosis, may show .their first evidence of 

 damage when they divide some time later and develop visible chromo- 

 somal defects and abnormalities. A high percentage of such cells may 

 die during this mitosis (Halberstaedter and Back, 1942; Kemp and Juul, 

 1930 ; Strangeways and Hopwood, 1926) . In some instances, the chromo- 

 somes may become "sticky" and pairs of chromosomes may adhere to 

 each other (Giese, 1947). If this occurs throughout the chromosomal 

 content of a cell, polyploidy may result. 



CHANGES IN TISSUES 



Nerve and muscle, two of the four major tissues, are relatively un- 

 affected by doses of radiation which elicit wide ranges of susceptibility in 

 the other two primary tissues, the various connective tissues and epi- 

 thelia. Some of the differences in sensitivity can be explained by the 

 fact that, in some tissues, resting cells and cells about to divide may 

 not show effects of damage until they divide. For example, in the 

 epidermis there are comparatively few cells dividing at any one moment, 

 and the full effects of irradiation do not become manifest until many of 

 the resting cells divide. Hepatic epithelium is normally untouched by 

 relatively large amounts of radiation. But if a large part of the liver is 

 removed, the rest will regenerate with great numbers of mitoses and 

 irradiation will affect the organ. 



The connective tissues differ from the other tissues in two important 

 respects: (1) the preponderance of intercellular substance, and (2) an 

 intimate relation to the blood vascular system (although cartilage and 

 parts of bone are exceptions). In all organs, to a greater or less extent, 

 connective tissue separates the blood vessels from the parenchyma. 

 Vascular connective tissue throughout the body is the tissue which 

 reacts, by inflammation, to local injury. Much has been written about 

 the effects of radiation on intercellular substances (see section on the 

 derma). In the hematopoietic tissues the free cells are many times more 

 susceptible to damage by irradiation than the cellular stroma. The 

 adipose, pigment, tendinous, and mucous connective tissues have not 

 been studied sufficiently for radiation effects. 



