20 DISEASES OF THE HOBSE. 



The force of the cough is considerable wlien it is not especially pain- 

 ful and when the lungs are not seriously involved. When the lungs 

 are so diseased that they can not be filled with a large volume of air, 

 and in heaves, the cough is weak, as it is also in weak, debilitated 

 animals. If mucus or pus is coughed out, or if the cough is accom- 

 panied by a gurgling sound, it is said to be moist; it is dry when 

 these characteristics are not present — that is, when the air in passing 

 out passes over surface not loaded with secretion. 



In the examination of the chest we resort to percussion and aus- 

 cultation. When a cask or other structure containing air is tapped 

 upon, or percussed, a hollow sound is given forth. If the cask con- 

 tains fluid, the sound is of a dull and of quite a different character. 

 Similarly, the amount of air contained in the lungs can be estimated 

 by tapping upon, or percussing, the walls of the chest. Percussion is 

 practiced with the fingers alone or with the aid of a special percussion 

 hammer and an object to strike upon known as a pleximeter. If the 

 fingers are used, the middle finger of the left hand should be pressed 

 firmly against the side of the horse and should be struck with the 

 ends of the fingers of the right hand bent at a right angle so as to 

 form a hammer. The percussion hammer sold by instrument makers 

 is made of rubber or has a rubber tip, so that when the pleximeter, 

 which is placed against the side, is struck the impact will not be 

 accompanied by a noise. After experience in this method of exami- 

 nation one can determine with a considerable degree of accuracy, 

 whether the lung contains a normal amount of air or not. If, as in 

 pneumonia, air has been displaced by inflammatory product occupy- 

 ing the air space, or if fluid collects in the lower part of the chest, 

 the percussion sound becomes dull. If, as in emphysema or in pneu- 

 mothorax, there is an excess of air in the chest cavity, the percussion 

 sound becomes abnormally loud and clear. 



Auscultation consists in the examination of the lungs with the ear 

 applied closely to the chest wall. As the air goes in and out of the 

 lungs a certain soft sound is made which can be heard distinctly, 

 especially upon inspiration. This sound is intensified by anything 

 that accelerates the rate of respiration, such as exercise. This soft, 

 rustling sound is known as vesicular murmur, and wherever it is 

 heard it signifies that the lung contains air and is functionally active. 

 The vesicular murmur is weakened when there is an inflammatory 

 infiltration of the lung tissue or when the lungs are compressed by 

 fluid in the chest cavity. The vesicular murmur disappears when air 

 is excluded by the accumulation of inflammatory product, as in pneu- 

 monia, and when the lungs are compressed by fluid in the chest 

 cavity. The vesicular murmur becomes rough and harsh in the early 

 stages of inflammation of the lungs, and this is often the first sign of 

 the beginning of pneumonia. 



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