NEUTRON EFFECTS ON ANIMALS 175 



layer of spermatogonia appeared normal but, in place of the normal gradual 

 formation of sperm from sperm.atogonia, the layer of primary spermato- 

 cytes was all in the same stage of mitosis. The secondary spermatocytes 

 stained faintly, the nuclei being uniform. Spermatozoa appeared normal. 



4th Day. Arrest of spermatogenesis (Fig. 6) was nearly complete with 

 the tubules containing spermatogonia, primary spermatocytes and a few 

 secondary spermatocytes. The lumina were filled with a homogeneous 

 pink-staining material, presumably a part of the Sertoli cells. The sperm 

 heads were frequently detached from the tail portion. A granular layer 

 frecjuently lined the tubules. The interstitial cells appeared to be normal. 



8th Day. The appearance was the same as on the 4th day. 



16th Day. The characteristic whorls of sperm tails seen in normal 

 testes were usually absent and there was little evidence of mitosis in many 

 of the tubules (Fig. 7). However, in some tubules the residual sperm ap- 

 peared morphologically normal. Scattered tubules were atrophic and 

 spermatogenesis was arrested in the primary spermatocyte stage. The 

 nuclei of these spermatocytes were frequently swollen and some spermato- 

 cytes were detached and were free in the lumina. \^acuoles occasionally 

 appeared among the layer of germinal cells but not within the cells them- 

 selves. Edema fluid surrounded the atrophied tubules and the interstitial 

 cells were enlarged. 



24th Day. There was an obvious decrease in the diameter of the tubules 

 (Fig. 8) in the center of the organ. These tubules contained masses of de- 

 generated cells in the lumina. The cells showed no evidence of mitosis 

 and the chromatin stained poorly. A few sperm heads and tails were dis- 

 tinguishable and a few multinucleated giant cells, along with vacuoles, 

 were present within the tubules. Nuclei of the Sertoli cells appeared 

 normal and there was an expansion of the cytoplasm. These changes did 

 not affect all tubules equally as there were a few tubules in which the 

 primary spermatocytes and sperm were intact, although there was no evi- 

 dence of mitosis. A few shrunken tubules consisted only of a single basal 

 row of cells of indefinite nature filled with amoi'phous bright red-staining 

 material. 



32nd Day. Numerous tubules were shrunken and showed no spermato- 

 genesis. They contained amorphous red-staining material representing, 

 in part, degenerated cells and, in part, syncytium of Sertoli cells. These 

 contrasted sharply with other tubules in which the first signs of regeneration 

 were present. A few mitotic figures were present in the layer of primary 

 spermatocytes. Edema fluid filled the spaces among the atrophied tubules 

 and the interstitial tissue was prominent. A few tubules contained multi- 

 nucleated giant cells and there were occasional vacuoles among the sperma- 

 tocytes. 



