Discrscs of the Heart and Organs of Circnlation. 301 



phied the impulse on the chest and pulse beat are equally weak. 

 When water exists in the pericardium the heart strikes the ribs 

 with less force. 



Sounds of the Heart. Synchronous with each beat of the 

 heart two distinct sounds are heard, separated by a short interval, 

 inappreciable to most ears, and followed by a period of silence. 

 These sounds are distinct alike in character and duration. The 

 first sozind is dull and prolonged ; the second is short and quick. 

 Some idea of these sounds w\z.y be formed by the pronunciation of 

 the two syllables, lub — tip, but an acquaintance with the sounds 

 themselves is essential to a correct conception of them. The pe- 

 riod of time occupied by the first sound is double that taken up by 

 the second and in man and the smaller quadrupeds the subsequent 

 period of silence is of equal duration with the second sound. Di- 

 viding the time belonging to one revolution of the heart into four 

 equal periods the first two are taken up by the first sound, the 

 third by the second sound and the fourth by the interval of silence. 

 In the horse the silence is more prolonged, and occupies the entire 

 latter half of the period of a revolution. The relations stand 

 thus : — the first sound extends over two-sixths of the time, the 

 second sound over one-sixth, and the silence over three-sixths. 



The_/?r^/ sound, sychronous with the beat of the heart against 

 the ribs corresponds also in point of time with the contraction of 

 the ventricles, the closure and tension of the auriculo-ventricular 

 valves and the rush of the blood into the great arteries. The sec- 

 ond sound corresponds to the reflux of blood in the arteries and 

 the closure of the valves between them and the heart. The period 

 of silence represents the period of rest during which the heart is 

 being filled from the veins. 



In the horse, at rest, the first is the only sound that can be 

 distinctly heard in many cases, but during the exci.emeut of ex- 

 ercise, or in febrile conditions the second is sufficiently apparent 

 and any deviation from the natural character is easily noted. 



These sounds are most distinct over the lower end of the fifth 

 and sixth ribs on the left side, but they may be heard distinctly 

 behind the middle of the shoulder on either side when the cor- 

 responding limb is advanced. In birds the\' may be heard be- 

 neath the wings but above all and most clearly over the breast- 

 bone. 



