DISEASES OF THE HEART, 



445 



tions made into its thickness sometimes show ingrowth of inter- 

 stitial connective tissue, which are dark-brown or marked with 

 spots or clear streaks (pigment ; fatty degeneration of the muscular 

 iibres), according to the duration of the process. On the surface of 

 these spots the muscle is soft and friable. When the right heart is 

 hypertrophied, if we make a traumatic section, its wall remains 

 rigid and its opening gaping. 



2. In simple or passive cardiac dilatation the heart is increased 

 in size by the enlargement of its cavities, and its walls are weak- 

 ened and edged off in proportion. It is mostly found on the right 

 side ; when existing in the left heart, if we make a transverse 

 section, the walls drop instead of remaining in a gaping condition. 

 Here, also, the structure of the myocardium may be normal, but, 

 as a rule, the walls are flabby, anemic, soft, friable, of a clear 

 yellow-brown color, affected by fatty degeneration ; at times they 

 are very thin, even transparent in certain places, where the two 

 serous membranes are directly back to back ; finally, as secondary 

 lesions, we may observe in the myocardium depressions to which 

 have been given the name cardiac aneurisms. Cases of dilatation 

 have been mentioned in which the size of the heart was more than 

 doubled. 



Etiology. Excentric hypertrophy of the heart depends upon 

 various causes : 



1. Violent exertions performed during work (idiopathic hyper- 

 trophy). This pathogenic influence is especially observed in race- 

 horses and hunting-dogs — animals making exertions of short 

 duration, it is true, but v/hich are pushed to their greatest intensity. 

 Reasons of the same kind determine that in a physiological state 

 the heart of horses of a fine breed is more voluminous than that 

 of common horses ; for instance, the heart of the thoroughbred 

 English stallion, ^^Helenus,'^ weighed nearly seven kilos. The 

 mechanism of idiopathic hypertrophy of the heart is that of mus- 

 cular hypertrophies in general : the contraction of the muscles of 

 the trunk during violent exertions determines a compression of the 

 muscular arteries, the blood can no longer flow therein so abun- 

 dantly, the arterial pressure increases and produces more violent 

 contractions of the heart, and as a consequence hypertrophy of the 

 myocardium results (Traube). 



In very nervous animals, especially in breeds of trained dogs, 

 we observe a special cardiac hypertrophy, the nature of which is 



