172 NEUTRON EFFECTS ON ANIMALS 



appearance of a typical section of a normal non-irradiated rat testicle is 

 shown in Figs. 1 and 2. 



11.3 n. No pathological change was observed prior to the 4th day after 

 completion of irradiation. 



4th Day. There was a decreased amount of spermatogenesis but no 

 disintegration of tissue. A few scattered tubules in the center of the organ 

 were slightly atrophied. 



8th Day. There were initial disintegration of spermatozoa and second- 

 ary spermatocytes and slight atrophy of the centrally located tubules. 

 The peripherally located tubules were normal in appearance. 



16th Day. The injury had progressed (Fig. 3); spermatogenesis had 

 ceased throughout the entire organ. The lumina were filled with de- 

 tached cells (probably secondary spermatocytes) and with fragmented 

 sperm. Edema fluid was prominent in the interstitial spaces, particularly 

 surrounding the atrophied tubules. 



24th Day. Damage was indistinguishable from that of the 16th day. 



32nd Day. Many of the tubules were extremely atrophied and con- 

 tained only Sertoli cells and spermatogonia. There was an abundance of 

 interstitial edema. Some tubules with mitotic figures in the primary 

 spermatocytes were present. 



45th Day. Atrophied tubules contained a homogeneous pink-staining 

 material. Interstitial cells were relatively prominent and apparently in- 

 creased in size. At the periphery of the organ many tubules were normal 

 in size and showed active mitosis. 



60th Day. Regeneration was well advanced in many of the tubules, 

 characterized by the formation of secondary spermatocytes and sperma- 

 tozoa. The remaining tubules were only slightly atrophied. 



75th Day. The entire organ appeared to be normal, except for a few 

 tubules which were somewhat atrophied (Fig. 4). All sections subsequent 

 to the 75th day were normal. 



56.4 n. No abnormal condition was observed prior to 24 hours after 

 irradiation. 



1st Day. A few tubules consisted only of multinucleated giant cells 

 (Fig. 5), primary spermatocytes and Sertoli cells. In these tubules sperma- 

 togenesis was incomplete. 



2nd Day. A number of tubules showed arrest or depression of spermato- 

 genesis in the secondary spermatocyte stage, characterized by many nuclei 

 of uniform size and of rather faint staining quality. There was some 

 vacuolization in some of these cells. 



3rd Day. Some tubules showed complete arrest of spermatogenesis. 

 The primary spermatocytes appeared to be normal but the secondary 

 spermatocytes were occasionally in abnormal mitosis. The basement 



