DISEASES OF THE CIRCULATORY SYSTEM. 193 



The pulse is small, feeble, and often irregular and inter- 

 mittent. 



Mitral Obstruction. — The clinical history of mitral 

 obstruction is similar to that of mitral regurgitation, with 

 which it is in many cases associated. In the horse we do 

 not know that the murmur characteristic of this disease in 

 man has ever been distinguished. This murmurin man imme- 

 diately precedes the systole, and is therefore termed pre- 

 systolic. It is due to the passage of the blood from the left 

 auricle through a constricted mitral orifice. 



Tricuspid Regurgitation. — In this disease, at each con- 

 traction of the right ventricle blood passes back through 

 the tricuspid valves into the right auricle, and thence into 

 the venae cavse and jugulars, which thus become rapidly 

 dilated and overloaded. 



A reflux pulsation in the jugulars with each ventricular 

 contraction is pathognomonic of tricuspid regurgitation. 



In this disease a systolic murmur is heard, as in mitral 

 regurgitation, but we cannot distinguish the two murmurs 

 in the horse. 



Aortic Obstruction. — When the aortic semilunar valves 

 obstruct the onflow of blood through the orifice, a murmur 

 is produced during systole. When they allow of regurgita- 

 tion back into the ventricle, the murmur is diastolic. 



When both conditions are present, both murmurs are 

 produced. In obstructive disease, the left ventricle hyper- 

 trophies to overcome the resistance ; but after a while the 

 mitral orifice, with the valves there, becomes involved, and 

 the equilibrium breaks down. In consequence of this, the 

 symptoms of mitral regurgitation are manifested. 



Aortic Regurgitation. — In this disease the blood-flow is 

 retarded; for after every contraction of the left ventricle, 

 part of the blood regurgitates back from the aorta into 

 the ventricle. The left ventricle therefore hypertrophies, 



13 



