294 Veterinary Medicine. 



into the artery, so that they allow blood to flow freely into 

 that vessel during the contraction of the ventricle, but prevent 

 any reflux into the heart when the ventricle again dilates. 

 The apparatus may be likened to a force pump with two systems 

 of valves, one to prevent the return of any water from the pump 

 into the fountain ; the other to hinder any reflux from the deliv- 

 ery pipe into the pump. Any interference with either of these 

 valves entails a very serious and usually a fatal disorder of func- 

 tion. 



These orifices differ considerably in size. Those between the 

 auricles and ventricles are considerably larger than those at the 

 commencements of the great arteries. Those on the right side of 

 the heart too are greater than those on the left. They vary with 

 the form of the heart. Thus in dilatation of an auricle and ven- 

 tricle on one side of the heart, the auriculo-ventricular opening 

 becomes equally widened and the valves remaining disproportion- 

 ately small the blood is allowed to rush back into the auricle dur- 

 ing ventricular contraction. The left auriculo-ventricular open- 

 ing has been known to become contracted in some very flat and 

 shallow chests ; the blood failing to circulate freely through the 

 lungs and to reach the left side of the heart in a full supply this 

 orifice accommodates its size to the amount, and may become so 

 narrowed that it forms a serious obstacle to the blood flow and a 

 series of morbid changes result following the backward course of 

 the circulation. The auricle first becomes overdistended and its 

 muscular walls increase in thickness and consistency ; the lungs 

 tend next to suffer from a passive congestion , and lastlv the right 

 side of the heart becomes engorged and enlarged. 



Any obstruction in the aorta which conveys the blood from the 

 left side of the heart equally leads to dilatation of its internal cav- 

 ity and abnormal thickness of its walls. 



The imperfection of the valves is one of the most serious results 

 of such changes in heart structure. The sounds by which such 

 imperfection may be recognized will be presently noticed, mean- 

 while the mode of testing this in the heart of the dead animal will 

 be referred to. If due to structural changes in the valves them- 

 selves, the new deposits, the cicatrices, the lacerations, etc. , will 

 be visible to the eye. Though no such disease changes are seen 

 the valves may still manifest imperfection by failing to fulfill 



