196 PHYSIOLOGY CHAP. 



This shows that the persistence of the centrifugal vortex produced 

 by the kinetic energy of the injected fluid, is of itself an adequate 

 mechanical condition to secure the perfect function of the valvular 

 apparatus, without the slightest regurgitation from ventricle to 

 auricle even if we admitted that presystole is not immediately 

 succeeded by systole, but that a period of intersystole constantly 

 intervenes, as has been proposed by Chauveau (infra, p. 201). 



V. The acoustic phenomena which accompany the cycle or 

 cardiac revolution are intimately connected with the valvular 

 . mechanism. 



When the heart of a healthy person is auscultated directly 

 with the ear or with the stethoscope, two distinct murmurs are 

 heard, known to physicians as the cardiac sounds. 



No one prior to Laennec (1819) had grasped the diagnostic 

 importance of these sounds. Harvey, whose panegyrists claim 

 that he was the first to describe them, confines himself to stating 

 that at the moment when the pulse is perceptible, a murmur can 

 simultaneously be heard in the chest. That is, he merely detected 

 the systolic sound, and rightly named it a murmur, since it has all 

 the properties of the latter, and can with difficulty be determined 

 as a musical tone. 



Nothing is easier under physiological conditions than to dis- 

 tinguish the first from the second sound: the first is longer, 

 deeper, duller ; the second is shorter, sharper, clearer. The second 

 sound is followed by a long pause, while between the first and 

 second there is a lesser pause. 



Since the first sound is systolic, i.e. it persists throughout 

 almost the entire systole, Laennec assumed that the first was 

 the effect of the systolic efflux from ventricles to arteries, the 

 second, of the diastolic afflux from auricles to ventricles, due to the 

 auricular systole or presystole. 



It was easy for Turner (1829) to refute the second part of this 

 theory, by showing that the second or short sound, since it succeeds 

 immediately to the first or long sound, coincides with the commence- 

 ment only of ventricular diastole (or perisystole), and cannot there- 

 fore be the result of the auricular systole (or presystole). 



Still more erroneous is Magendie's theory (1835), which 

 assumed that the first sound was the effect of the impact of the 

 apex of the heart against the thoracic wall in systole, and the 

 second of the impact of the base during presystole. The sounds 

 persist even after the thoracic cavity has been opened, and the 

 heart exposed. 



The so-called valvular theory of cardiac sounds was first 

 formulated by Carswell and Eouanet (1832). Starting from the 

 correct observation that the first sound is more acute in the region 

 of the ventricles, and the second in that of the arterial orifices, 

 they admitted that the first depended on the vibrations of the 



