THE MOTION OF THE BLOOD. 173 



at the moment of the pulse of the arteries, at least of those 

 nearest the* heart, is heard a dull sound ; and immediately after- 

 wards, without any interval, a clearer sound, similar to the noise 

 of a valve or to the licking of a dog. The first sound occupies 

 about | of the whole time; the second sound or ^, and then a 

 pause occurs of about another J. This is termed the rhythm of the 

 heart's action. The sounds of the heart are ordinarily heard in 

 health between the cartilages of the fourth and seventh left ribs, 

 and under the inferior part of the sternum ; those of the left side 

 of the heart in the former situation, and those of the right in the 

 latter. The first sound is usually loudest at the lower part of 

 the heart's region; the second, at the higher part, in the situation 

 of the auricles. 



Whatever may be the cause of these sounds, the first occurs 

 at the moment the ventricles contract : for it occurs at the instant 

 the aorta receives blood from the left ventricle; and we know 

 that both ventricles contract simultaneously. We might presume 

 that the second sound occurs at the moment the auricles contract, 

 and that therefore the auricles part with their blood immedi- 

 ately after the action of the ventricles. Again, when we reflect 

 that the moment the ventricles have contracted, they relax, as is 

 proved by our feeling and seeing the walls of the chest instantly 

 recover their position after being forced outwards by the stroke 

 of the heart, and as their relaxation is the production of a cavity 

 for the blood of the auricles, we may hence be certain that 

 the auricles discharge their blood into the ventricles instantly 

 after the ventricles have discharged theirs. 



In truth, those who open living animals assert that they see 

 the apex of the heart recede from the walls of the chest, and 

 the ventricles expand, instantaneously after their contraction, and 

 that, at this moment of expansion, the blood rushes into them from 

 the auricles, and a retractile motion of the auricles occurs most 

 observable at the sinus." It requires no vivisection to show that 

 this must be the case. 



m See the lamented Dr. Laennec's immortal Work, Traite de V Auscultation 

 Mediate, et des Maladies des Poumons et du Cceur. (Edit. 1. 1819.) Edit. 3. 



The force and extent of the sounds and shock, and the rhythm of the heart's 

 action, are variously altered in disease, and other sounds superadded, resembling 

 that of a bellows, a file, a saw, a drum, a dove, &c. , all highly interesting to a phi- 

 losophic mind, and indispensable to be known to all practitioners but empirics. 



n Dr. Hope's Treatise on the Diseases of the Heart and Great Vessels, London, 

 1832. p. 40. 



N 



