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aorta would flow freely into them as well as into and through the intra- 

 mural arteries, capillaries and veins. According to Brucke the partial empty- 

 ing of the coronary arteries and their intra-mural branches, and the consequent 

 fall of pressure within them toward the end of the diastole facilitates the 

 systole of the ventricles, while the filling of the vessels and the consequent 

 rise of pressure promotes the diastole. This anatomic mechanism and its 

 associated functional activity constituted according to Brucke an apparatus 

 by which the activity of the heart could be self -regulated. This view as to 

 the time of the filling of the extra-mural coronary arteries has, however, been 

 disproved. 



At the present time it is generally believed as the result of many forms 

 of experimentation that the extra-mural coronary arteries are filled during 

 the time of the systole. For it has been shown that the semilunar valves do 

 not close the openings of the coronary arteries by reason of the presence of 

 blood behind them under a high pressure; that a division of one of the 

 branches of these arteries is followed by a spurt of blood synchronous with 

 the systole. Moreover, if a kymographic trace of the pressure within the 

 coronary artery be compared with the trace of the pressure within the 

 carotid artery, it will be found that there is a complete agreement between 

 them as the pressures in the two vessels rise and fall simultaneously and 

 as a corollary are filled during the systole. Because of the pressure which 

 the heart-muscle must exert upon the smaller arteries and veins within its 

 own substance during systole, it is probable that there is a temporary retarda- 

 tion of the flow of the blood during the systole in the coronary (the extra- 

 mural) vessels, followed by a return of the velocity during the period of 

 diastolic repose. 



During the diastole the blood flows freely from the extra-mural vessels 

 into the intra-mural arteries and capillaries. It is at this time too that the 

 heart-muscle receives from the capillary blood-vessels its nutritive material 

 and returns to the blood the products of its metabolism. During the systole 

 the intra-mural capillaries and veins are compressed and the blood driven 

 into the extra-mural veins. The greater the force and frequency of the beat, 

 the larger the volume of blood passing through the coronary system. 



Vaso-motor Fibers for the Coronary Arteries. The presence in the 

 vagus and sympathetic nerves, of vaso-motor fibers for the coronary arteries 

 has been a subject of much investigation and discussion. By reason of the 

 fact that stimulation of these nerves modifies the rate and the force of the 

 heart-beat, and these in turn modify the flow of blood through the vessels, it 

 is difficult to state whether the observed effects are the result of changes in 

 the caliber of the arteries or to a change in the character of the heart-beat. 

 Moreover owing to the anatomic relation which the arteries bear to the heart 

 muscle, the rapidity of the flow through them must vary with each contrac- 

 tion and relaxation and thereby the difficulty of interpretation is increased. 

 The results of direct experimental investigations of Porter, however, lead to 

 the conclusion that the existence of vaso-motor (constrictor) fibers for the 

 coronary arteries is highly probable. 



These investigations have been corroborated by the investigations of 

 Barbour and Prince who have found that when isolated monkey hearts are 

 perfused with autogenous hirudin blood diluted with Locke's solution con- 

 taining minute doses of epinephrin, the coronary flow is decreased. From 



