PTTLSB 193 



Sounds of the heart. — If one listens carefully to the heart beat, 

 by placing the ear against the chest, two distinct sounds may be 

 distinguished. The first is lower in pitch than the second and 

 of longer duration. It is supposed to be produced by two factors, 

 the vibration of the tricuspid and mitral valves in closing, and the 

 vibration of the contracting muscle mass. The second sound is 

 sharper and is due to the closing of the semilunar valves. The 

 first sound is essentially a systolic sound, while the second is dia- 

 stolic. These two sounds are of great aid to the physician in deter- 

 mining cases of heart trouble. For detecting variations in this 

 sound an instrument called the stethoscope is used, and this method 

 of examination is called auscultation. 



Pulse. — When the ventricles contract the blood is 

 forced into the arteries with a spurt. If the arteries, 

 capillaries, and veins were rigid tubes this sudden pressure 

 would be transmitted instantaneously throughout the 

 entire system, and a quantity of blood would enter the 

 auricles exactly equal to that which left the ventricles. 

 Owing to the elasticity of the walls of the blood vessels 

 this is not the case. Part of the pressure is used up in 

 expanding the walls. Since the arteries are subject to 

 the most direct effect of this systole the reason for their 

 thicker walls is apparent. This elastic character of the 

 arteries also results in the pressure being transmitted in 

 a wave instead of directly. The results of this may be 

 pictured as follows: As the ventricle contracts the ex- 

 pressed blood stretches that portion of the artery nearest 

 the heart. As the ventricle expands and this pressure is 

 removed this enlarged part of the artery begins to contract 

 slowly, and the pressure is transferred to another point 

 further along in the artery. As the next systole occurs 

 this process is repeated, and thus the effect of the pressure 

 or wave is gradually transmitted throughout the whole 



EDDY. PHYS. — 13. 



