246 PHYSIOLOGY. 



of the ventricles, with, of course, greater tension of the auriculo- 

 ventricular valves. 



Increase of the second sound denotes a higher tension in the 

 corresponding large arteries. The condition is usually demonstra- 

 tive of overfilling and congestion of the pulmonary circuit. With 

 equal intensity the muscular sound of the left ventricle is appre- 

 ciably longer than that of the right. 



Weak heart-sounds are indicative of a feeble action of the heart 

 and usually denotes degenerations of the heart-muscle. 



The first sound is very faint or not heard at all when the 

 ventricular systole is weak. If the ventricle is hypertrophied the 

 sound is low and booming; if the heart-muscle is dilated, the sound 

 is high pitched. 



The Coronary Arteries. The heart-muscle, by reason of its 

 almost constant activity, must be very generously supplied with blood 

 to insure its proper nutrition. In it are found a system of arteries, 

 capillaries, and veins, known as the coronary vessels. 



The arteries going to the heart-muscle are two in number: the 

 right and left coronary. They are the first branches of the aorta, and 

 take their origin just above the level of the free margins of the semi- 

 lunar valves. The diameter of the coronary arteries is that of a 

 crow's quill. From these main vessels there proceed numerous 

 branches which dip down into the heart-substance, dividing and sub- 

 dividing as they go until a system of capillaries is formed. 



The effete products are conveyed to the general circulatory sys- 

 tem by the coronary vein, which empties its blood into the right 

 auricle. 



It, with its branches, is provided with valves, since every auricular 

 systole interrupts the venous flow; the ventricular contractions, 

 however, accelerate its flow. The coronary arteries are characterized 

 by their very thick connective tissue and elastic intima, which perhaps 

 accounts for the frequent occurrence of atheroma of these vessels. 



The net-work of cardiac capillaries is very close and spiral vessels 

 are found which supply blood in the change of form and position by the 

 muscle-fiber. The coronary arteries do not anastomose. 



Porter found the volume of blood passing through the coronary 

 vessels is increased by an increase in either the force or the fre- 

 quency of the heart-beats. The emptying of the intra-mural vessels of 

 the heart by the contraction of the heart favors the flow of blood 

 through the heart walls chiefly by the diminished resistance which the 

 empty patulous vessels offer to the inflow from the aorta when the 



