Materials and Methods

Catala~ e Experiments.--Mice from Charles River Breeding Laboratories, North Wilmlngtion, Mass. weighing 25-30 g and maintained on a standard laboratory chow, were used. Beef liver catalase was obtained as a twice crystallized aqueous suspension with 0.1% thymol as preservative (Type C-100, Sigma Chemical Co., St. Louis, Mo.). Various batches contained between 20-27 mg/ml. Before use, the bottle was shaken with a rotatory motion to avoid frothing, and a uniform suspension of all sedimented crystals was obtained. The amount of catalase needed was then pipetted off and warmed in a water bath at 37-40 C until it became clear. A few minutes of ultrasonic vibration in a" Maxomatic" ultrasonic vibrator (L and R Manufacturing Co., Kearny, NJ) at the same temperature was sometimes necessary to effect solution. Prolonged heating was avoided to prevent denaturation of catalase. In some experiments NaC1 was then added to the catalase solution to achieve a concentration of 0.85%. The experimental findings were the same whether or not the injected solution contained isotonic NaCI. The osmotic effect of the catalase itself, was considered negligible. Mter centrifugation to remove a faint turbidity that sometimes formed after addition of NaCI, the solution was injected into the tail vein. 0.5-0.7 ml of solution containing a standard dose of 13.5 mg was injected slowly over a period of 5 rain. A few animals were given higher doses, from 20 to 27 rag.~[ice were sacrificed 1, 5, 30, 69, 90 rain and 3, 6, and 12 hr after injection. The kidneys were removed under ether anesthesia and thin slices were fixed by immersion for 3 hr at room temperature in 2% paraformaldehyde: 2.5% glutaraldehyde in 0.1• cacodylate buffer, pH 7.4, containing 0.05% CaC12 (17). Tissues were then washed overnight in cold 0.1~ cacodylate buffer, pH 7.4, and sections 40# thick were cut on a TC-2 Smith-Farquhar tissue chopper (Ivan Sorvall, Inc., Norwalk, Conn.). The sections were collected in 0.05~ tris (hydroxymethyl) aminomethane (rris)-HC1 buffer at pH 8.5, and incubated at 37 C for 2 hr in a medium consisting of 10 mg 3, 3'diaminobenzidine tetrahydrochloride (Sigma Chemical Co., St. Louis, Mo.) dissolved in 10 ml of Tris-HC1 buffer at pH 8.5. A dialysis bag containing 25 mg of BaO~ in 1 ml of Tris-HCl buffer was used as the peroxide source (15). After incubation, sections were washed twice in buffer, postfixed for 90 rain in 1.3% OsO4 in 0.2~ s-collidine buffer at pH 7.4, and embedded in Epon after rapid dehydration. Thick sections were cut on glass knives and viewed unstained. Thin sections, cut on glass or diamond knives, were examined unstained, or lightly stained with lead citrate, in a Philips