Microscopically, changes are quite common and varied in character. In the seminiferous tubules, the changes range from a slight desquamation of the germinal epithelium to atrophy and complete degeneration of the entire tubule, as was the case in the left testis of Bull 1. In the mild cases, spermatogenesis occurs apparently in a normal manner up to the spermatid stage, at which point many of the cells degenerate and slough off. These appear in the seminal fluid, associated with the few sperms that reach maturity. This sloughing and degeneration may be localized in a few of the tubules, or it may be widespread over the entire organ. Likewise, the changes may involve not only the more mature cells, but they may be so severe as to cause almost total degeneration and desquamation of the seminal epithelium, as in Fig. 15. These defects in spermatogenesis are of course evidenced in the semen by the presence of immature, or abnormal types of sperms. With cessation of spermatogenesis or degeneration of the epithelium of the entire gland, no sperms are formed. Not infrequently one finds numerous tubules, or even the entire testis in which the germinal epithelium is intact, but there is little or no evidence of mitosis, as in some tubules of Bull 6. The cells are several layers deep as in the normal condition, but they are not dividing. This condition is shown in Fig. 13. In the more chronic forms, the tubules become atrophied, and frequently disappear entirely. The membrana propria may become thickened, due to excessive connective tissue formation, or infiltration with serum or exudate. On the other hand, a distinct atrophy may occur. The stroma of the organ not infrequently is thickened by inflammatory exudates, or by a noticeable increase in the connective tissue. In some testes, the connective tissue is so much increased that the tubules rapidly become atrophied, and disappear. In abscess formation, due to acute inflammations, the entire organ becomes enlarged, markedly hyperaemic, and infiltrated with leucocytes. Necrotic areas appear here and there in the parenchyma. The rete often shows a marked degeneration of the lining epithelium, and atrophy caused by increase of the interstitial connective tissue.