THE SEMIL UNAR VAL FES. ! 3 



He supposed that the intraventricular negative pressure, which is known to 

 exist, Avas systolic in time. He helieved that the hlood, aided by its momentum, 

 was shot out with a velocity which the ventricular wall could not follow. To 

 this fact he ascribed the origin of the negative pressure, which, in its turn, 

 produced the closure of the valves, and that before any regurgitation could 

 take place. This theory is entirely unsupported by the curves of intra- 

 ventricular pressure. 



The position of the semilunar valves during the time of systolic 

 output has been a subject of considerable controversy. An old doctrine 

 of Thebesius was revived by Briicke. 1 He maintained that the valves 

 swing back against, and close, the orifices of the coronary arteries during 

 the systolic period. Thus, he taught, the heart is only fed with blood 

 during diastole. While, in systole, the w T ant of blood brings the con- 

 traction to a close, the re-entry of blood in diastole leads to the 

 expansion of the heart. 



The publication of this doctrine led to a fierce discussion, but Briicke 

 defended his position with such brilliancy and wealth of argumentative 

 resource, that for a time his theory was accepted by most of the schools. 

 Meanwhile, several anatomists chronicled cases in which the valves 

 were not sufficiently large to cover the coronary orifices, and in these 

 no abnormality of the heart had been observed during life. Chauveau 

 and Eebatel 2 finally overthrew Brucke's theory by simultaneously 

 measuring the velocity and the pressure in the coronary artery. The 

 former was recorded by means of Chauveau's instrument, the hsemo- 

 dromograph (see " Velocity of Flow," p. 85). 



At the beginning of systole the velocity and pressure in the coronary 

 arteries increase ; later, the velocity becomes negative, and the pressure 

 rises, or, in other words, the blood begins to flow in the reverse direction 

 back to the aorta. At this stage the ventricular wall is so strongly 

 contracted that the muscular tension rises above that of the aorta; 

 the coronary arteries and their tributaries are therefore compressed, 

 and the blood driven back into the aorta. In the final stage, when the 

 diastole is commencing, the velocity once more increases. 



By Newell Martin and Sedgwick 3 the pressures in the coronary 

 artery and the aorta were synchronously recorded. They found that 

 the coronary tracing was always a duplicate of that of the aorta. 



We may conclude, then, that the coronary arteries are not closed by 

 the valves, but that the cardiac vessels are compressed within the 

 muscle, and emptied back towards the aorta. This is confirmed by 

 experiments of Klug, 4 who ligatured the base of the heart in the period 

 of systole, and again in the period of diastole. In the systolic heart the 

 vessels within the deeper layers of the musculature w r ere found to be 

 emptied of blood. Injection of the coronary arteries with fluid at 

 the pressure of the aorta having been found to produce a negative 

 pressure in the cavity of the ventricles, we must admit the truth 

 of part of Brucke's hypothesis. Each systole does partially cut 

 off the heart muscle from its blood supply, and at each diastole the 

 injection of the coronary arteries does aid in the dilatation of the heart. 



1 Sitzungsb. d. k. AJcad. d. Wissensch. tnath.-naturw. CI., Wien, 1855, Bd. xiv. S. 345 ; 

 " Der Verschluss der Kranzscldagadein durch die Aortenklapprii," Wien, IS.".."'. 

 - " Rech. expt'r. sur la circ. dans les arteres coronaires," These, Paris, 1872. 



3 Journ. Physiol., Cambridge and London, 1882, vol. iii. p. 165. 



4 Ccntralbl. f. d. vied. Wissensch., Berlin, 1876, S. 133. 



