254 BIOLOGICAL EFFECTS OF IONIZING RADIATIONS 



(2) The long-term damage may prove to be greatest in the chromosomes, 

 at mitosis, but such genetic effects may not appear for several gen- 

 erations. 



(3) Damage to the fine network of molecular membranes and canals in 

 the cell's substructure, where the enzyme-controlled protein and nu- 

 cleic acid syntheses take place, can result in immediate physiological 

 changes. Damage to cell walls and structural tissue is important at 

 high dose or after some time at low dose. 



EFFECTS OF WHOLE-BODY IRRADIATION 



The Facts and the Complexity of the Problem 



Three events, each horrible in its own way, provide the foundation of our 

 knowledge about whole-body irradiation of normal humans. The first was 

 the bombs at Hiroshima and Nagasaki; the second was an accident at Oak 

 Ridge, and others, less publicized, later; and the third, unpredicted winds 

 over Bikini and the Marshall Islands during H-bomb trials. 



Three months after the publication by Roentgen of his experiments with 

 X rays, puzzling radiation burns on the skin were observed. Within a few 

 years, premature loss of hair and early ageing befell the early workers. From 

 ten to forty years after intense exposure, some gruesome cancers appeared, 

 and case histories showed they could be attributed to the exposures long 

 before. 



Careful analyses, now sixteen years in progress, of the results of the atom 

 bombs over Japan, have yielded much modern clinical experience with 

 radiation-induced epilation, premature ageing, and cancer. The effects re- 

 sulted principally from gamma rays and neutrons given off by fission prod- 

 ucts. In the Marshalls it was principally betas from heavy hydrogen (tri- 

 tium). At Oak Ridge two scientists died slowly from a 600-rad accidental 

 exposure during a demonstration of thermonuclear fusion, and half a dozen 

 more received severe, but sublethal, doses. All these cases were very care- 

 fully documented. 



Studies on animals have mushroomed in the past decade. The guinea- 

 pig, pig, mouse, dog, goat, monkey, rat, hamster, and rabbit: all have con- 

 tributed their bit to the phenomenology. Various interesting things have 

 been learned. For example, if any tissue is selectively protected by shield- 

 ing, usually a substantial increase in the animal's LD 50 occurs. In mice, pro- 

 tection of a hind leg, or the intestine, or the head, or the liver, but particu- 

 larly the spleen, causes significant increase in the LD 50 . In the larger ani- 

 mals, the results of protection (shielding) of the long bones, the site of red 

 blood cell synthesis, have been spectacular. As a corollary, irradiation of 

 specific tissues and organs in the larger animals has shown (1) the great 



