SPECIAL CLINICAL EXAMINATION. 83 



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

 cussion hammer we are unable to determine the boundaries 

 of the organ, the adjacent lung tissue so modifying the sound 

 that the merging of the dull sound of the heart's percussion 

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



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

 region of the 4th and 5th 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. 



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

 and 7th ribs can be determined by vigorous percussion. 



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. 



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. 



The Auscultation of the Heart. 



Method. The auscultation of the heart may be practiced by 

 placing the right ear just behind the left elbow, the leg being 

 drawn forward. Small animals may be laid upon the table and the 

 phonendoscope used. 



Physiology. In the cardiac region and in the neighborhood of 

 the same, we hear at each action of the heart two tones. One 

 of these tones appears at the moment the organ contracts {sys- 

 tole), and the second tone, which quickly follows the first, at the 

 dilation of the organ {diastole). The second tone follows so 

 closely the first one that it is diflficult to differentiate between 

 them, except in animals which carry a pulse below 60. In ani- 

 mals which have rapid pulse it may be necessary to compare the 

 pulse at a peripheral artery with the heart's beat. 



The origin of the heart-tones is still subject to dispute, the 

 authorities not agreeing. 



