SPECIAL CLINICAL EXAMINATION. 85 



3. Where the lung between the heart and the chest wall 

 becomes thickened. 



The heart's beat is weakened: 



1. When the force is enfeebled from degeneration of 

 the heart's muscle. 



2. Where the heart is crowded away from the chest wall 

 Ivy accumulations of exudate in the thoracic cavity (pleuritis, 

 pericarditis), or in some cases of pulmonary emphysema or 

 tumors. 



Percussion of the heart. Except in very thin animals 

 (horses) the percussion of the heart is of no great value in 

 the diagnosis of disease, the reason being that with the percus- 

 sion hammer we are unable to determine the boundaries of the 

 organ, the adjacent lung tissues so modifying the sound that the 

 merging of the dull sound of the heart's percussion into the full 

 sound of the lung's is a very gradual one. 



Horse. In the horse, under favorable circumstances, in the 

 region of the 4th and Sth intercostal space a zone of dullness 

 about the size of a hand can be brought out by percussion. Its 

 boundaries, however, are generally indefinite. 



Ox. Although the chest walls are thinner in this animal, the 

 heart is covered more by the lungs than in the horse. 



Sheep and Goats. A slight dullness is noted over the fifth 

 rib. 



Dog. A narrow horizontal line of dullness between the 4th 

 and 7th ribs can be determined on both sides by vigorous per- 

 cussion. 



Due to unfavorable anatomical position, the percussion 

 of the heart is of diagnostic service only in a few instances. 



The zone of cardiac dullness is in- 

 creased in hypertrophy of the heart and where fluids col- 

 lect in the pericardium; tumors and thickenings of the lungs 

 also induce it. 



The zone of cardiac dullness is some- 

 times decreased from pulmonary emphysema because 

 the distended lung extends further over the heart. 



A tympanitic tone on percussion over the cardiac 

 region is obtained in traumatic pericarditis of the ox, gases 

 of putrefaction accumulating in the pericardium. 



The percussion of the cardiac region causes the animal 

 pain in pleuritis and pericarditis. 



