Morphological and histochemical studies on the cardiac conduction system of the dog.

According to the physiological and morphological studies of the cardiac conduction system by PURKINJE (1945), ENGELMANN (1894, 1895, 1897), HIS (1893), TAWARA (1906), KEITH and FLACK (1907) and others, the stimulation of the heart occurs at the conduction system and is conducted through this specialized system but not through the ordinary muscle. Although GLOMSET and his coworkers (19401952) postulated on the basis of their observations that conduction system of the heart was not "specialized", but a part of the ordinary heart muscle, and that stimulation of the heart spreads over the heart not through the "specialized" muscular tissue, but through the intracardiac nervous tissue, this neurogenic theory was denied by WALLS (1947), TRUEX and COPENHAVER (1947), COPENHAVER and TRUEX (1952), BAIRD and ROBB (1950), KUGLER and PARKIN (1956) and others. Today, myogenic theory of the conduction is widely supported by morphologists and physiologists. In spite of many investigations, many questions are still open about the conduction of the stimulus in the heart, especially about the mechanism of the conduction. A large amount of glycogen has been observed in the cardiac conduction system since the last part of the 19th century (MARCHAND 1885, ASCHOFF and NAGAYO 1908 and others). But the physiological meaning of glycogen in the conduction tissue is not yet clear. Recently, cases of heart block occuring after the open-heart surgery, have attracted considerable attension among cardiologists (LAUER et al. 1959, CALLAGHAN et al. 1961, and others). To avoid this complication, knowledge of the localisation and branching of the cardiac conduction system becomes necessary. Iodine method (TAUFIC et al. 1954, ALLEN et al. 1959 and others) and modified periodic acid-Schiff reaction (OTSUKA and HARA 1965) seem useful to visualize the atrioventricular system macroscopically. In the present paper, cardiac conduction system of the dog is reported morphologically and histochemically with special reference to following points: 1) histological difference between specialized conduction system and ordinary cardiac muscles, 2) morphological connection of the specialized tissue and ordinary cardiac muscles, 3) peripheral ramification of the atrioventricular system, and 4) differences in character and amount of glycogen between the specialized and ordinary heart muscles.