Abstract
After a single injection of cortisone acetate into 4-week-to 8-month-old BALB/c, DDD, ICR-JCL, ddy-SLC mice, lesions in the heart showing characterized by white flecks located predominantly on the surface of the right heart ventricle (Photo 1) were observed with a high incidence (Table 1) when the animals were killed 10 days later.
Histopathologically basophilic granular degeneration and severe destruction in myocardial fibers adjacent to the pericardium were observed (Photo 2) . Degenerated myocardial fibers were enlarged and nuclei disappeared in many of them. Many of these cells contained a number of basophilic microgranules. Rarely vacuolar and edematous degeneration was found (Photo 2) . Around the coronary artery the lesions were associated with multiplication of fibroblasts (Photo 2) . Basophilic granules in degenerated area were shown to be PAS positive and resistant to salivery digestion (Photo 7) .
By Kossa's stain multifocal calcium deposits were shown in degenerated myocardial fibers as well as in connectve tissue (Phot 5, 6) .They were associated with multiplication of fibroblasts, collagen fibers and occationally mononuclear round cells.
Such cardiac lesions were considered to be due to the dystrophic calcification and not to calcareous metastasis because calcification was not observed in elastic fibers of alveolar wall, renal collecting ducts and stomachal mucous membrane. Calcium and inorganic phosphorus contents were not elevated in the sera of the affected mice (Table 2) .
No organisms were detected from affected lesion by incubating on horse blood agar. Serum agglutinin against Corynebacterium kutscheri and Salmonella enteritidis and CF antibodies to Tyzzer's agent and MHV (Pr) were negative with 1 : 8 sera of affected mice, while CF antibodies to Sendai virus were positive in some cases. In mice which were injected intravenously with 0.1 ml of affected heart emulsion (1: 20) no cardiac lesions were observed. However, further observations are needed to determine whether HVJ infection is involved for producing the heart lesion.
