CONTRIBUTION TO THE PATHOLOGY OF THE CARD IAC SINUATRIAL NODE IN HORSES

From the right atrium of 56 slaughter horses without obvious cardiac d isease the area of the sinuatrial node (Keith-Flack-Node) was dissecte d and fixed in 10% buffered formalin. After fixation four tissue block s were embedded in paraffin, from which serial sections were prepared. The stains applied were Hematoxylin-Eosin, connective tissue stains a nd the PAS-Alcianblue reaction. All alterations present in the atrial myocardium and the sinuatrial node were recorded. The following lesion s were seen: fibrotic-dystrophic foci in the wall of the right atrium (all cases), focal ossifying myocarditis (4 cases), lymphocytic myocar ditis (1 case), proliferation of connective tissue (2 cases), atrophy of nerve fibers (5 cases), and slight fibro-elastic intima proliferati on in small arteries (10 cases).