This was attempt to find the developmental process of Pneumocvstis carinii pneumonia. The 28 rats divided two group, 24 experimental group and 4 control group. In experimental group, the rats were injected with 5 mg of prednisolone twice a week for 6 weeks intramusculary and drinking water contained 500 mg oxytetracyline per liter. Control group was not administered at all.
The 4 rats were sacrified at each week in experimental group, control group was sacrified at 6 weeks later. The specimens of rat lung observed macroscopically, and then stamp specimens were made of Giemsa, toluidine blue 0 and gram staining preparations. For microscopic observation, the lung was fixed with 10％ buffered neutral formalin, and then made Giemsa, Gomori´s methenamine silver and hematoxylin-eosin staining preparations.
The results were obtained as follows：
1. The body weight of experimental group were markedly depressed, and macroscopic finding of infected lung seemed liver like appearance.
2. Cysts of Pneumocystis carinii in staining preparations were first demonstrated at 2 weeks later in experimental group.
3. Grade 3 of Pneumocystis carinii pneumonia was first demonstrated at 4 weeks when the rats were injected with 5 mg of prednisolone twice a week.
4. Histopathologic findings of hematoxylin-eosin staining preparations were found in order of infiltration of lymphocyte, thickening of alveolar septum, infiltration of macrophage, eosinophilic foamy exudate, desquamation of alveolar lining cell, fibrinoid degenration and so on, but plasma cell andPneumocystis carinii were not found.
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