CARDIAC MURMURS. 545 



aj)preciablc period of rest, to which succeeds the systoHc sound 

 again. 



The first sound, whatever caused by, is coincident with the 

 contraction of the ventricles and the impulse of the heart 

 against the walls of the thorax. The second sound corresponds 

 with diastole of the ventricles and the recedence of the heart 

 from the side. 



The natural sounds may in disease be variously modified. 

 (a) They may be altered in intensity and power, being either 

 increased and prolonged, as in hypertrophy, excitation of 

 the heart's action, and in some blood-changes ; or they may be 

 diminished and lessened, as in weakness, atrophy, and degener- 

 ative changes of the muscular structure of the heart, (b) They 

 ma}^ be modified in character or quality ; the tones may be 

 high-pitched and clear, or muffled and indistinct, (c) Their 

 rhythm or regularity may be destroyed, as in diseases of the 

 valves and orifices. 



B. Cardiac Murmurs. — More strikingly abnormal, however, 

 than the alteration of the natural sounds are those which in 

 disease we find so often added to them, the so-called cardiac 

 murmur's. These may occur in conjunction with one or 

 other of the natural sounds, or they may altogether usurp their 

 place. 



From their supposed origin, or the mode in Avhich these 

 sounds or murmurs are produced, they are spoken of as — 

 (1) Valvular or endocardial ; (2) Pericardial oy exocardial. 



1. Endocardial or Valvular Sounds. — These sounds as a 

 class give out a uniform hloivlng, rasping, or hellovjs character, 

 from which impression they have come to be spoken of as 

 bellows-murmurs. They are called valvular sounds because of 

 their nearly uniform origin from valvular defect or disease. 



The chief structural changes from which these bellows- 

 murmurs are supposed to proceed are — (a) Simple dilatation 

 of natural orifices; (6) Simple contraction of natural orifices-; 



(c) Simple roughness of valvular or endocardial surfaces; 



(d) The association of either of the former conditions with the 

 latter. 



Valvular murmurs, when believed to be associated with any 

 of these conditions, are spoken of as structural or organic 

 murmurs, to distinguish them from abnormal murmurs not 



35 



