568 CHRONIC DISEASES OF THE HEART. 



CHAPTER XXX. 



CHRONIC DISEASES OF THE HEART. 



I. Enlargement of the Heart — Hypertrophy and 

 Dilatation. 



Definition. — An unnatural development of the muscular ivalls 

 of the heart, augmenting its bulk hy increase of the muscular 

 structure, and generally accompanied with increase of the 

 cavitary capacity. 



Meaning of Terms. — Enlargement of the heart, increase of its 

 bulk from increase of the muscular structure, and dilatation 

 of one or more of its cavities, has in the horse attracted the 

 attention of the majority of observers for a lengthened period ; 

 but attempts to connect these changes with particular symp- 

 toms exhibited during life have, from anatomical and other 

 difficulties, been sparingly attempted, and not always success- 

 fully. 



The auricles or ventricles may severally be the seat of this 

 extra growth, or the venous or arterial heart may each in 

 different cases be more particularly involved. The superior 

 cavities or auricles are much less frequently the seat of this 

 enlargement or increase of their walls, and probabl}^ the left 

 ventricle is more liable to the change than the right. 



When affecting the heart sectionally or in parts, we speak of 

 it as partial hypertrophy ; Avlien the entire organ is involved, as 

 general hypertrophy. Cardiac enlargement may be regarded 

 as resulting from two general conditions : 1. Increase in bulk 

 of the muscular walls ; 2. Increase of cavitary capacity — dila- 

 tation. 



As these conditions rarely exist uncomplicated, but are 

 variously related to each other as to extent, the state of en- 

 largement has been named in accordance with these relation- 

 ships. 1. SimiJle hypertrophy, when the increase in bulk is 

 unassociated with alteration of cavities. 2. Simj^le dilatation, 

 when there is increase of cavitary capacity without increase of 

 bulk of muscular tissue in walls, or with thinning of these. 

 3. Hypertrophy with dilatation — eccentric hypertrophy — when 

 there is increase of muscular structure with increase of capacity 

 of cavities ; sometimes the hypertrophy is in excess of the 



