It includes a serological classification of strains isolated from organ material and a study of the cytopathogenic effect of the viruses in cell cultures of the kidneys and lungs of pig embryos and of the kidneys of bacon pigs and calves. MATERIAL AND METHODS The cell cultures of embryonic kidneys and lungs and of the kidneys of newly-slaughtered bacon pigs were grown in Hanks BSS with 0.1 % yeast extract, 0.5 % lactalbumin hydrolysate, 10-15 % calf serum and antibiotics. When a confluent

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... yer had developed, the medium was renewed with a corresponding medium of Earles BSS, but containing only 1 % calf serum.