128 The Lymphocyte and Lymphocytic Tissue 



After irradiation with 2000 r or more, some rabbit lymphocytes develop 

 nuclear abnormalities such as bilobed and trilobed nuclei. 50, 51 About one to 

 two hours after irradiation, both the lymphocytes with normal nuclei and 

 those with lobed nuclei undergo sudden acute death with only slight changes 

 in morphology. I have called this change "death by delayed fixation." On 

 further incubation, the "fixed" lymphocytes undergo post-mortem autolytic 

 changes characterized by slow shrinkage of the nuclei and blurring of the 

 chromatin pattern. 



The human lymphocyte was observed to undergo the same cytologic 

 changes as the rabbit lymphocyte, i.e., intranuclear vacuolization after 1000 

 r or less and death by delayed fixation after 2000 r or more. The recently de- 

 veloped slide chamber method"' 1 was used to study the rate of death of 

 irradiated and nonirradiated human lymphocytes. According to this method, 

 the in vitro longevity or the 10 per cent survival time of nonirradiated 

 human lymphocytes was found to be, on the average, 9.2 days. After irradi- 

 ation with 1000 r, the lymphocytes from 19 individuals had a 10 per cent 

 survival time of from 1.1 to 2.2 days with an average of 1.7 days."' 2 Irradiation 

 even with 5 r decreased appreciably the 10 per cent survival time. These 

 experiments show that human lymphocytes are highly radiosensitive and 

 that there is relatively slight variability in the sensitivity of the lymphocytes 

 from different individuals. 



Tests were also made on the blood lymphocytes of 31 patients with chronic 

 lymphocytic leukemia or lymphosarcoma with leukemia. 54 The nonirradi- 

 ated leukemic lymphocytes had an average 10 per cent survival time of 10 

 days. The lymphocytes after irradiation with 1000 r had 10 per cent survival 

 times which varied from 0.3 to 10 days. It is particularly important to observe 

 that 7 of the 31 leukemic patients had lymphocytes with 10 per cent survival 

 times greater than 2.5 days. In other words, about 20 per cent of the patients 

 had blood lymphocytes that were resistant to x-rays. The significance of the 

 radioresistance of the lymphocytes in these patients is still under study. 



It was surprising to find that the leukemic lymphocytes of most of the 

 patients had approximately the same radiosensitivity as normal lympho- 

 cytes. Block"' studied the effect of x-rays in patients with leukemia or 

 lymphoma by means of serial biopsies of the spleen. He concludes, "There 

 is no evidence to support the commonly held belief that malignant cells are 

 more sensitive to x-irradiation than the corresponding nonmalignant cells." 

 The in vitro and the in vivo findings are in accord. 



It is necessary to consider the radiosensitivity of lymphocytes of different 

 species in order to know to what extent animal findings can be extrapolated 

 to man. The problem is complicated by the surprising finding that the 10 

 per cent survival time for the nonirradiated lymphocytes of the human is 



