124 



DISEASES OF THE RESPIRATORY ORGANS 



(Fig. 57). Lay the plate close to the wall of the chest, and, with the hammer 

 in the other hand, strike the plate a number of light, quick taps; the fingers 

 can also be used, and are preferred by some. Place the index or middle 

 finger of the left hand firmly on the chest wall, and with the index finger 

 of the right hand tap on the finger of the left hand. 



The limits of percussion arc given in Fig. 58, but it must be taken into 

 consideration that on expiration the posterior limit of the lungs is carried 

 forward of the dotted line and not extending to the last rib and also that 

 when the stomach or intestines are very much filled with gas, and crowd 

 the diaphragm forward, the extent of the lungs is lessened. The per- 

 cussion area lies in a triangular space between the lower side of the mus- 



FiG. 58. — Field of percussion; x, location of heart beat. 



cles of the back, the posterior portion of the muscles of the forearm, and 

 the ends of the ribs, and by pulling the forelegs forward, the extent of the 

 chest wall can be increased for examination. In percussion we make the 

 distinction between a clear, loud, normal lung sound and a tympanitic, 

 dull, or solid sound of a diseased lung. The clear normal sound of the 

 healthy lung is heard all over the thorax, the volume of sound depending 

 on the thickness of the lung at the particular part being examined. The 

 muscular layers of the chest have a certain effect on the sound, very thick 

 walls lessening the sound to a certain extent; the soimd is more or less 

 dull over the shoulder-blade, sterum, and back; the posterior borders of 

 the lungs often have no perceptible sound, as they are so thin. 



