THE HEART BEAT. 491 



grammeters of work. That is, the mechanical work done at each 

 contraction of the heart is equal to that necessary to raise 288 gms. 

 a meter in height. The calculations made by different authors as 

 to the amount of blood discharged from each ventricle during 

 systole may be tabulated as follows: 



Thomas Young 45 gms. 



Volkmann 188 



Vierordt 180 



Fick 50-73 



Howell and Donaldson 75-90 



Hoorweg 47 



Zuntz 60 



Tigerstedt 50-100 



Plumier 70 



Loewy and v. Schrotter .... 55 



for weight of 72 kgms. 



65 



60-65 kgms. 



The Coronary Circulation during the Heart Beat. The 



condition of the blood-flow in the coronary vessels during the phases 

 of the heart beat has been the subject of much speculation and 

 experiment, since it has entered as a factor in the discussion of 

 several mechanical and nutritive problems that are connected with 

 the physiology of the heart. According to a view usually attributed 

 to Thebesius (1708), the flaps of the semilunar valves are thrown 

 back during systole and shut off the coronary circulation, and 

 therefore the coronary vessels, unlike those of other organs, are 

 filled during diastole. In modern times this view has been revived 

 by Briicke, who made it a part of his theory of the " self-regulation" 

 of the heart beat. According to this view, the coronaries are shut 

 off from the aorta during systole by the flaps of the semilunar valves, 

 so that the contraction of the ventricle is not opposed by the 

 distended arteries, while, on the other hand, the reinjection of these 

 vessels from the aorta during diastole aids in the dilatation of the 

 ventricular cavities. Experimental work has shown decisively that 

 the part of this theory relating to the closure of the coronary arteries 

 by the semilunar valves is incorrect.* Records of pressure changes 

 in the coronary arteries during the heart beat made by Martin and 

 Sedgwick and by Porter show that they are substantially identical 

 with those in the carotid or aorta, and records of the velocity of the 

 blood-flow made by Rebatel show that at the beginning of systole 

 the flow in the coronaries suffers a sudden systolic acceleration as in 

 the case of other arteries. During systole, therefore, the mouths of 

 the coronary arteries are in free communication with the aorta. 

 But the coronary system arteries, capillaries, and veins is in 

 part imbedded in the musculature of the ventricles, and we should 

 suppose that the great pressure exerted by the contracting muscu- 



* See Porter, "American Journal of Physiology," 1, 145, 1898, for dis- 

 cussion and literature. 



