28 THE MECHANISM OF THE CIRCULATION. 



suction of blood would have no perceptible effect on the auricular 

 pressure. 



There is some evidence of two phases of negative pressure in the ventricle, 

 one very short in duration, appearing very early in diastole, the other pre- 

 systolic in time, and lasting longer. This latter has been ascribed by Cliauveau 

 and Marey to the aspiration of the thorax, acting on the heart at a time when 

 the tone of the muscle had decreased. The whole subject of the intraventri- 

 cular negative pressure is still in obscurity ; all that can be said is, that we are 

 certain that a negative pressure usually appears, though we do not know why it 

 is inconstant and variable. We are uncertain whether it has any effect on the 

 filling of the ventricle, and must suppose that its origin is complex, depending, 

 probably, on the elastic rebound of the walls, on the filling of the coronary 

 arteries, and especially on the aspiration of the thorax. 



THE HEART SOUNDS. 



The existence of these sounds was not concealed from Harvey. He 

 writes : " When there is the delivery of a quantity of blood from the 

 veins to the arteries a pulse takes place, and can be heard within the 

 chest." l To Laennec, 2 the founder of the art of auscultation, is owing 

 the first accurate description of the character of the sounds and their 

 significance in the diagnosis of diseases of the heart. To the ventricular 

 contraction he ascribed the first sound, and the second sound to the 

 auricular contraction. The second sound he aptly compared to the 

 sound produced by a dog lapping water. Laennec's authority remained 

 unquestioned until Turner 3 pointed out that the second sound occurred, 

 not at the end but at the beginning of the diastolic pause, and therefore 

 could not derive its origin from the auricular systole. He suggested 

 that the second sound might be caused by the dilatation and suction 

 action of the heart at the end of systole. From then till now the cause 

 of the sounds has been a subject of endless controversy. Dunglison, 4 

 in 1856, tabulated the opinions of a large number of authors, showing 

 what an extraordinary amount of discordance has existed upon this 

 matter; nor is there even yet a consensus of opinion on the ques- 

 tion. Sandborg, in 188 1, 5 collected as many as forty different 

 theories. 



That so many theories should have arisen is not surprising, since so 

 many different phenomena attend each contraction of the heart, any one 

 of which may be capable of producing a sound. The mistake has been 

 that each observer, according to his particular theory, has attributed 

 the sounds to one simple factor, and has failed to recognise that the 

 sounds are in reality not pure tones but are compound in origin. Thus 

 the first sound has been ascribed to the following causes : 



1. The impulse of the heart against the parietes of the thorax. 



2. The rush of blood through the narrowed orifice of the aorta and 

 pulmonary artery. 



3. The contraction of the muscular wall of the ventricles. 



1 "De motu Cordis," ch. v. 



2 "De 1'auscultation mediate," Paris, 1819, tome ii. p. 210. 



3 Trans. Mcd.-Chir. Soc. Edinburgh, 1829, p. 226. 



4 "Human Physiology," 1856, vol. i. p. 140. 



5 " Resume" des etudes sur les bruites du coeur," Christiania, 1881, p. 6. 



