THE HEART 253 



commodated in the auricles. This is in fact one of the 

 distinct services performed by these chambers. When 

 the above-mentioned valves open the auricles are very 

 full and a rapid redistribution of blood between the 

 auricles and the ventricles must take place in the first 

 part of the ventricular diastole, (n) in Fig. 55. There 

 are therefore two times in the cycle when the blood 

 moves at an accelerated pace into the ventricles: first 

 when the valves open to admit it from the overfilled 

 auricles and; second, when the active contraction of the 

 auricles thrusts on the latest portion of the ventricular 

 charge. 



The Heart Sounds. Each heart-beat is attended by 

 the production of two sounds which have long been 

 closely studied because of their relation to the recog- 

 nition of disease. To the trained ear of the physician 

 their subtle variations are most significant. In a book 

 like this we can give them only a little space. The first 

 is described as a prolonged low-pitched and booming 

 note; the second is higher in pitch and has a staccato 

 character. It may be called a click. It can be shown 

 that the first sound occurs during the systole of the 

 ventricles and the second comes at the close of this 

 phase. 



It is believed that the first sound, long represented 

 by the syllable "lubb," has a somewhat complex origin. 

 We have, entering into it, a muttering from the tense 

 walls of the ventricles, the rush of blood through the 

 outlets, and perhaps the humming of the taut valves 

 which are preventing a return to the auricles. If either 

 the mitral or the tricuspid valve is imperfect and there 

 is any considerable reflux from one of the ventricles 

 during their systole the first sound will be altered. 



The second sound is usually reproduced by the syllable 

 "diip." Its origin is quite clear: it is the snap of the 

 semilunar valves as they close at the beginning of the 

 ventricular diastole. It can be reproduced in a lifeless 

 preparation by injecting fluid backward into the artery 



