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The histopathology and serum levels of mice inoculated intravenously with Pseudomonas aeruginosa exotoxin were studied. The toxin exerted a marked effect on the liver but elicited no demonstrable microscopic changes in other organs. The microscopic lesions caused in the liver by a single injection of two 50% lethal doses (LD50) of toxin (2.3 mug) were characterized by necrosis, cellular swelling, and fatty change within 4--8 hr and near total hepatocellular necrosis at 48 hr. Hepatic necrosis was accompanied by a parallel rise in serum levels of aspartate and alanine aminotransferases and alkaline phosphatase. A single injection of 10 LD50 elicited similar but somewhat more rapid degeneration. No progressive lesions were seen after injection of toxoid or of 0.5 LD50 of toxin.

Abstract. Five cases of arnebiasis were diagnosed in goldfish (Carassius auratus) from home aquariums and from a laboratory aquarium. Granulomas containing amoebae were in many organs but were most numerous in kidneys. Because there were pseudopods, food vacuoles, vesicular nucleoli and other ultrastructural characteristics of the organisms, we identified the organisms as amoebae. On the basis of mitotic stages it is possible they belong in the family Hartmannellidae.