182 NEUTRON EFFECTS ON ANIMALS 



that the relatively long experimental period allowed nearly complete re- 

 covery of the spleens. 



B. Histopathological Changes. Three groups of 20 or more adult, male 

 white rats, each rat weighing 180 to 250 grams, were irradiated in Box 

 No. 7. One group received a single dose of 11.3 n in a period of 12 minutes. 

 A second group received 56.4 n in a period of 1 hour. The 3rd group re- 

 ceived a total of 113 n, administered in 2 equal doses on successive days. 

 Immediately after irradiation and at various intervals up to 200 days, 

 representative rats from each group were killed by a blow on the head and 

 the tissues placed in Bouin's fluid. Sections were stained with hematoxyUn 

 and eosin. The results are reported in 3 parts according to dose. 



11.3 n. During the first 4 days after irradiation there was no observable 

 change. 



8th Day. The Malpighian corpuscles were slightly smaller than normal. 

 The germinal centers were slightly less active than normal and contained 

 a small amount of cellular debris and blood pigment. 



16th Day. The germinal centers were approximately normal in size, 

 but the zone of surrounding l^miphocytes was slightly narrower than nor- 

 mal. Cellular debris and blood pigment were present. 



24th Day. The Malpighian corpuscles were nearly normal in size and 

 the surrounding tissue contained numerous polymorphonuclear leukocj^tes. 



32nd Day. Polj^morphonuclear leukocytes were distributed throughout 

 the tissue. An occasional monocyte filled with blood pigment was ob- 

 served; otherwise the organ appeared to be normal. Tissues taken subse- 

 quent to the 32nd day were normal. 



56.4 n. Immediatel}' after irradiation the germinal follicles and the 

 zones of l^^mphocytes were normal in appearance, but the surrounding pulp 

 contained numerous polymorphonuclear leukoc3'tes, occasionally arranged 

 in small groups. 



4th Hour. The Malpighian corpuscles were reduced in size and there 

 was necrosis in the germinal centers. This was accompanied bj' slight 

 neutrophilic infiltration. Cellular debris was present, but necrosis was 

 most marked in the germinal centers. Lymphoid tissue showed no evi- 

 dence of mitotic activity. 



8th Hour. The Malpighian corpuscles were small. Cellular debris was 

 present and was being phagocytosed. IMonocytes were distended Avith 

 blue staining particles. 



24th Hour. The follicles were smaller and showed no evidence of mi- 

 totic activity. There were only a few recognizable germinal centers. 

 Blood pigment was present (Fig. 18). A section of a normal spleen is 

 shown in Fig. 17. 



2nd Day. The IVIalpighian corpuscles were so small that their presence 

 was indicated only by small masses of lymphocytes around the arteries 



