(1) Hematological and histopathologic changes were studied in dogs and rats after infusions of solutions of methylcellulose.

(2) After 4 to 8 weeks of daily intravenous infusions of 0.6 Gm. of 400 centipoise methylcellulose, the dogs developed moderate anemia with a reduction of the mean red cell volume to 27 ± 4 cc./Kg., compared with 38.6 ± 3 cc./Kg. in the controls, and a reduction in the apparent red cell life span studied with Cr51 from 24 ± 3 days in the controls to 18 ± 3 in the treated animals.

(3) Following the infusions in the dog there was an increase of the mean blood urea nitrogen from 15 mg. per cent to 96 mg. per cent, with only a small increase in the rat.

(4) At necropsy there was foamy cytoplasmic vacuolization throughout the reticuloendothelial systems of both rat and dog. In the dog, the spleens were pale and moderately enlarged. Large cells with vacuolized cytoplasm largely replaced the normal structures of this organ. In the markedly enlarged rat spleen there were islands of methylcellulose-filled cells, surrounded by a rim of lymphocytes and strikingly engorged red pulp.

In the rat there was vacuolization of the renal glomerular cells but no significant change in the tubules or interstitial tissue. In the dogs sacrificed one week after the termination of the methylcellulose infusions, foamy cytoplasmic distention of the glomeruli and interstitial cells and tubular dilatation and cyst formation were noted. Progressive fibrosis and hyalinization of the glomerulus and fibrosis and calcification and lymphocytic infiltration of the interstitial tissue were seen in the kidneys of dogs sacrificed from 3 months to 3 years after termination of the methylcellulose infusions.

(5) Although methylcellulose infusions produce splenomegaly and anemia in the dog, the associated uremia precludes this preparation as a model for the study of hypersplenism.

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