412 Veterinary Medicine. 



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 sound is dull and prolonged ; the second is short and quick. 

 Some idea of these sounds may 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 period 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. Dividing 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 pro- 

 longed, 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 first 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 

 second 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 excitement of 

 exercise, or in febrile conditions the second is sufiiciently ap- 

 parent 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 

 corresponding limb is advanced. In birds they may be heard 



