One hundred pneumonic lungs from calves were examined by an immunoper oxidase technique using avidin-biotin- per oxidase complex method in formalin-fixed, paraffin-embedded sections for Haemophilus somnus. In the histological examination of tissue sections, strong positive reactions against H. somnus were detected in 14% of the lungs. H. somnus antigens were observed at the surface and/or within the epithelial cells, macrophages, necrotic alveolar walls, alveolar -bronchial/br onchiolar exudates, fibrins, distended interlobular septa and perivascular areas. In addition, dense antigen accumulations were detected in the necrotic macrophages and neutrophils.

One hundred pneumonic lungs from calves were examined by an immunoper oxidase technique using avidin-biotin- per oxidase complex method in formalin-fixed, paraffin-embedded sections for Haemophilus somnus. In the histological examination of tissue sections, strong positive reactions against H. somnus were detected in 14% of the lungs. H. somnus antigens were observed at the surface and/or within the epithelial cells, macrophages, necrotic alveolar walls, alveolar -bronchial/br onchiolar exudates, fibrins, distended interlobular septa and perivascular areas. In addition, dense antigen accumulations were detected in the necrotic macrophages and neutrophils.