94 AUTOMATIC REGULATION OF THE HEART. 



taneous pulsatory elevations. In accordance with these observations is the fact 

 that an incised coronary artery spurts continuously, with systolic exacerbations, 

 as do all other arteries/ 



4. If a strong stream of water is passed intermittently through a sufficiently 

 large tube introduced into the left auricle of a fresh pig's-heart, and it is forced, 

 through the auriculo-ventricular orifice on into the aorta; and if the aorta beyond 

 its arch is connected with a large tube directed upward (in order to establish 

 pressure in the aorta) , the water will be seen to spurt continuously from the 

 divided coronary artery, with systolic exacerbations. 



5. There is constantly present in the sinuses of Valsalva an amount of blood 

 sufficient to fill the arteries in question during systole. 



6; The valves when elevated are not applied closely against the wall of the 

 aorta, even with the greatest amount of pressure that can be exerted by the 

 ventricle. On the contrary, there remains between each valve-leaflet and the 

 aortic wall a semilunar space filled with blood, as is shown in Fig. 24. 



7. Undoubted cases of extensive destruction of the semilunar valves that 

 with certainty render closure of the mouths of the coronary arteries impossible 

 are directly opposed to this theory. 



8. Observations on muscle have shown that during contraction its small 

 vessels undergo dilatation and the blood-stream through it is accelerated. It is, 

 therefore, difficult to believe that in the contracted heart-muscle the movement 

 of the blood should cease. 



As, during the systole, the small arterial branches lying close to the 

 ventricular cavity are exposed to a pressure greater than that of the 

 aorta a systolic compression of their lumen occurs, with a forcing out 

 of their contents in the direction of the veins. The ventricular con- 

 traction thus aids the flow of the blood in the coronary vessels ; marked 

 dilatation of the heart diminishes it. 



The capillary vessels of the myocardium are numerous in correspond- 

 ence with the energetic activity of the heart; they, like the small vessels 

 generally, lie within the muscle-bundles in contact with the muscle- 

 cells. With their transition into veins several of them coalesce almost 

 at once to form a large vein, from which the extremely easy passage of 

 the blood into the veins is readily understood. The veins are provided 

 with valves. As a result it happens that (i) with 'the systole of the 

 right auricle (therefore during the ventricular diastole) the venous 

 stream is interrupted; (2) with contraction of the ventricle the flow of 

 blood in the cardiac veins is accelerated in the same way as it is in the 

 veins of the muscles. This systolic acceleration of the venous flow 

 permits of the conclusion that the arterial circulation is not interrupted 

 at this time. 



The coronary arteries, between which no anastomoses occur, are characterized 

 by the great thickness of their elastic and connective-tissue intima, and this per- 

 haps explains the frequency of calcification in these vessels. Many of the lower 

 vertebrates have no vessels in the heart-substance (anangiotic hearts) for example, 

 the frog; but this statement is disputed. 



The motor disturbances and even the complete cessation of action 

 that have been observed in the heart after partial or complete occlu- 

 sion of the coronary vessels are of importance, particularly as analogous 

 conditions are observed in man in consequence of occlusion or narrowing 

 of the coronary arteries (for example, as a result of calcification). 



Method. In rabbits, under the influence of curare and with artificial respira- 

 tion, or after previous section of the vagi (in order to exclude the inhibitory 

 influence of this nerve), it is possible to clamp off the coronary arteries close to 

 their origin from the aorta with a spring clamp. Ligation is less satisfactory, as 

 it cannot be accomplished without wounding the heart. In dogs it is possible 

 to push a glass rod provided with a button-like extremity from the subclavian 



