1126 RADIATION BIOLOGY 



body) and these sometimes persist for three weeks or longer (Pierce, 

 1948). At 30 minutes mitosis has ceased and there are varying degrees 

 of nuclear swelling and clumping of the chromatin in all cells of the 

 villous, crypt, and Brunnerian epithelium. Collapsed goblet cells appear 

 to be more numerous than normal. The most extreme damage is in the 

 basal cells of the crypts of Lieberkuhn, where nuclear fragmentation and 

 karyolysis are present for some days. Mitotic figures reappear at 21 

 hours, but until 9 days degenerative changes can be detected in the epi- 

 thelium. At this time regenerative changes become dominant, as evi- 

 denced by disappearance of degenerating cells, the presence of the usual 

 number of mitotic figures, and crowding of the basal crypt cells. The 

 Paneth cells, which have lost their normal staining properties 2 hours 

 after irradiation, show irregular granulation until 9 days. 



The epithelium of Brunner's glands, which is apparently more resistant 

 than the villous or crypt epithelium, does not show marked degenerative 

 changes with this dose until the 8-hour interval. However, recovery 

 seems to be less rapid ; in some animals the tubules are still distended at 

 21 days. 



After 800 r (total-body) the destructive process in the epithelium of 

 the ileum is less severe but is qualitatively similar to that of the duodenum 

 and recovery is more rapid. Mitotic activity of the crypt epithelium, 

 absent 30 minutes after exposure, is restored at 3 days. Degenerative 

 changes are most marked in the basal crypt cells. There is only very 

 slight nuclear damage in the epithelial cells of the colon and rectum. 

 Increased mucus secretion, which is suggested, is difficult to evaluate 

 because of normal variations in this function. Stafford L. Warren 

 believes that the colon is about as sensitive as the stomach and that the 

 more resistant rectum is about as sensitive as the mouth. 



Early effects in the lamina propria are edema and absence of inflam- 

 matory cellular reaction. At 2 hours the number of small lymphocytes is 

 reduced, and many of the lymphocytes show degenerative change. How- 

 ever, there is less destruction of lymphoid cells here than in the lymphatic 

 follicles, for many appear to survive. There is a return of lymphocytes 

 and plasma cells after 9 days. The effects on the lymphatic follicles of 

 the ileum and appendix are much like those described in the lymphatic 



tissue. 



After 400 r in the rabbit the damage is qualitatively similar to that 

 produced by 800 r but quantitatively less severe, with fewer cells affected 

 and earlier recovery. One hundred roentgens causes only a depression 

 of mitosis and occasional dead crypt cells. Doses of 50 r or lower produce 

 no effect. 



Total-body exposure of rabbits and mice to fast neutrons and of mice 

 to slow neutrons has the same qualitative effect on the intestinal mucosa 

 as total-body X irradiation. 



