(a through e) Histological sections of kidneys. Kidneys from mice were fixed in 10% formalin, embedded in paraffin, sectioned at 4 μm, and stained with hematoxylin and eosin. Representative sections as viewed under low power magnification (200×) from (a) a normal mouse (N), (b and c) phenylhydrazine-treated mice that survived, and (d and e) immunohistochemical analyses of kidney sections from phenylhydrazine-treated mice using a rabbit antiserum against mouse Hb. The presence of Hb was indicated by the brown precipitates. The glomeruli of phenylhydrazine-treated mice appeared relatively normal. Representative sections as viewed under high power magnification (400×). (f and g) Mice that survived the phenylhydrazine treatment; (h and i) mice that died during phenylhydrazine treatment. Hydropic degeneration, as evident by the numerous vacuoles, was observed. Arrows indicate Hb precipitates and M indicates metaphase cells found in histological sections of kidneys from phenylhydrazine-treated mice that survived. The mitotic index was calculated by randomly selecting 6 low power fields; within each low power field, the number of metaphase nuclei was counted against the total number of nuclei in 6 randomly chosen high power fields. Kidney sections from two mice of each genotype (+/+ and −/−) that survived the phenylhydrazine treatment were used to quantitate the mitotic index. The average mitotic index ± SD for +/+ mice was 18.8 ± 4.3 per 1,000 nuclei versus 4.78 ± 3.2 per 1,000 nuclei for −/− mice.