AUSCULTATION. 529 



Other valuable indications may be obtained by coughing 

 the animal. The deep inspirations which precede and follow 

 a cough will often bring out indistinct sounds into greater 

 prominence, and enable us to decide as to their character. 

 The clearing of the air-passages which results from coughing 

 will likewise temporarily remove certain sounds, such as the 

 mucous rale, by obviating their cause. 



In auscultation, be it remembered, that though sounds are 

 generally heard in greatest intensity closest to their seat of 

 origin, yet, by travelling through condensed pulmonary tissue, 

 they may reach the ear at a considerable distance with nearly 

 their primitive force. Such a source of fallacy will often be 

 corrected by the indications yielded on percussion. 



PERCUSSION. 



The methods of performing this operation have already 

 been indicated (see page 499.) It remains to mention the 

 sounds elicited in healthy and diseased conditions of the 

 chest. 



In all parts of the healthy chest, when the proper sub- 

 stance of the lung comes into contact with the thoracic 

 walls, a clear sound is elicited on percussion. This varies 

 with the force of percussion. Thus, when the surface is 

 lightly struck, the sound though low is clear, proceeding 

 only from the more superficial air-sacs. When a stronger 

 impulse is made over a part containing a considerable thick- 

 ness of lung tissue, the sound is louder and even somewhat 

 sonorous. If the patient be lying, the sound may be modi- 

 fied by the character of the bed ; thus it will be more reson- 

 ant in an animal reclining on a hard surface than on a soft 

 yielding material. To a certain extent the sounds on the one 

 side may be taken as a criterion by which to judge the con- 

 dition of the opposite ; but this is to be received with con- 



2M 



