130 MANUAL OF EQUINE MEDICINE. 



Crepitation. — Crepitation is produced by the bursting of 

 air-bubbles in fluid, and is spoken of as large, medium, 

 and small, according to the supposed site of the bubbles 

 which produce them. Crepitation has, therefore, been spoken 

 of as moist sounds in contradistinction to rhonchus and 

 sibilus, which are dry sounds. 



Very fine crepitation is, however, probably due to the 

 separation of the walls of the air-vesicles in inspiration, 

 when, as the result of pressure or collapse, they have been 

 in partial contact. Crepitation similar to this, but not 

 similarly produced, is also occasionally heard over emphy- 

 sematous lungs. 



Rhonchus and Sibilus. — These sounds are due to 

 vibration in the air, through bronchial tubes in which the 

 mucous membrane has become altered or roughened by 

 inflammation or secretion. 



Rhonchus is produced in the large tubes and is deeper 

 in tone. It is described as a snoring, cooing, or 

 grating, according to its special character in diff'erent in- 

 stances. 



Sibilus is produced in the smaller tubes, and is a wheezing 

 noise, more hissing in character than rhonchus. 



2. Pleural Friction. — In health the surfaces of the pleurae 

 are smooth, and move upon each other without producing 

 any sound. When the pleurae are roughened by disease, 

 the rubbing of the two roughened surfaces i^roduces a 

 sound to which the name of * friction' is applied. Friction, 

 being produced in the pleura, sounds close under the ear, 

 and is double, owing to the movement of the lungs to 

 and fro. 



It may be very limited in extent. 



When efi'usion into the pleural cavity takes place, the 

 surfaces of the serous membranes are separated, and the 

 friction thus disappears ; but when the inflammation sub- 



