DISEASES OF THE CIRCULATORY SYSTEM. 191 



number of the muscular elements, is general or partial. It 

 may be attended by thinning of the walls and dilatation of 

 the cavities, when it is called eccentric atrophy ; or it may 

 occur without alteration in the capacity of the cavities, 

 when it is called simple atrophy. . There is much weakness 

 with feeble cardiac impulse, which is felt only over a 

 small area ; but there are no diagnostic symptoms of this 

 condition. 



CHRONIC VALVULAR AFFECTIONS. — Valvular 

 disease may arise from acute or chronic endocarditis; 

 from atheromatous or calcareous changes; from enlarge- 

 ment of the orifices ; and, lastly, from congenital mal- 

 formations. 



It has been already mentioned that disease of the valves 

 may allow of regurgitation of blood owing to insufficient 

 closure ; or may cause obstruction to the onflow of the 

 blood, owing to constriction or partial blocking of the 

 orifice, resulting from adhesion of the valves or thickening 

 of the structures around the opening. 



Each orifice is then capable of each kind of disturbance : 

 regurgitation and constriction. There may be theoretically, 

 therefore, eight kinds of murmurs, viz. : (1) Aortic regurgi- 

 tation and constriction ; (2) Mitral regurgitation and con- 

 striction ; (3) Pulmonary regurgitation and constriction ; 

 (4) Tricuspid regurgitation and constriction. 



Auscultation is attended with great difficulty in the horse, 

 and, in consequence, our means of diagnosing valvular 

 affections are far more limited than in man. 



Disease of the left side is more common than on the right. 

 In disease of the valves of the left side, the pulse is altered 

 in character and rhythm ; while in disease of the right side, 

 the chief manifestations are in the venous circulation. 

 Jugular pulsations are very commonly visible, and dropsical 

 effusions and anasarcous swellings liable to follow. Yet it 



