1022 PHYSIOLOGY 



diseases affecting the valvular orifices of the heart, this vibration may 

 occur during every heart cycle and be heard with ease on applying 

 the ear to the chest. These murmurs, or bruits as they are called, 

 are of paramount importance in enabling the medical man to form 

 a judgment as to the condition of the different valves of the heart. 

 Thus injury to an aortic valve, so as to allow of leakage during diastole, 

 involves the squirting of a small amount of fluid under high pressure 

 from the aorta into the relaxed ventricle. On listening to the chest of a 

 man with such a lesion this regurgitation during diastole is heard as a 

 rushing sound occurring in the place of or continuing the second 

 sound up to the beginning of the next first sound which denotes the 

 beginning of systole. 



In many cases the disease which occasioned the inadequacy of the 

 valve is followed by processes of repair and cicatrisation in which the 

 valves become puckered and contracted and perhaps adherent, so 

 that the orifices can never become thoroughly patent or thoroughly 

 closed. Under such circumstances vibrations will be set up in the 

 current of blood as it escapes through the narrow orifice into the 

 aorta during systole, and on listening to the chest over the second 

 right costal cartilage a ' to and fro ' bruit is heard composed of a 

 systolic immediately followed by a diastolic murmur. In the same 

 way incompetency of the mitral valve or of the mitral orifices, in 

 consequence of weakness of the cardiac muscle, gives rise to a murmur 

 which lasts during the whole of the ventricular contraction and is 

 therefore systolic in character. Such a murmur is heard best over the 

 apex beat, and is also transmitted backwards so that it can be heard 

 on listening at the back of the patient. A narrowing of the mitral 

 orifice in consequence of contraction of the valves will set up a resist- 

 ance to the flow of blood from left auricle to left ventricle. The auricle 

 becomes hypertrophied, its contraction prolonged, and the escape of 

 blood through the contracted orifices gives rise to a murmur which is 

 heard on listening over the apex beat as a presystolic bruit. This 

 bruit is easily distinguished from a systolic murmur by noticing that 

 it runs up to and ends with the apex beat, whereas a systolic murmur 

 does not begin until the elevation of the apex commences. 



Several physiologists have succeeded in recording heart sounds graphically. 

 Hiirthle's method consists in an application of the microphone. A special form 

 of stethoscope is so arranged that by its means the vibrations corresponding to 

 the heart sounds are transmitted to a contact between silver and carbon. Through 

 this contact a strong current is passing. This also passes through an electro- 

 magnet, which attracts an iron disc attached to the membrane of a Marey's 

 tambour. Any vibration transmitted to the carbon-silver contact alters its 

 resistance, and so the strength of the current passing through the electro -magnet. 

 In this way the heart sounds can affect the pull exerted by the electro -magnet 

 on the membrane of the tambour, and the change in the volume of the contained 

 air is recorded by means of an ordinary registering tambour. 



