DISEASES OF THE RESPIRATORY ORGANS. 127 



sounds along the bronchi and small tubes, and their modifi- 

 cation by having to pass through the vesicles, or it may be 

 due to both these causes. 



It is a characteristic soft breezy murmur, heard in 

 inspiration and expiration, between which there is an 

 appreciable interval. The expiration is very faint or in- 

 audible. The murmur is louder in the young than in aged 

 animals, and may be heard in the horse over the greater 

 part of the chest, and is most distinct in well-bred horses, 

 and in those in which the chest-walls are not loaded 

 with muscle and fat. 



Changes in the Breathing Sounds in Disease : 



1. In the Anterior Air-Passages. — In some horses the 

 nasal sound is abnormally increased in exercise. This 

 sound is louder in expiration than in inspiration. It is 

 best heard during trotting or cantering gently, and usually 

 disappears when the horse is going at a good steady gallop. 



It arises from the flapping of the nostrils, and constitutes 

 what is improperly termed ' high-blowing.' Professor Wil- 

 liams says, ' I have repeatedly observed that some horses 

 will emit the sound when first put into work after resting a 

 while, but wdien brought into condition the sound entirely 

 ceases, and I have thought that the sound was due to flaccid 

 condition of the dilatores naris muscles.' 



High-blowing may also be due to narrowness of the nasal 

 apertures and passages. 



These conditions as they do not interfere with the useful- 

 ness of the horse, cannot be said to constitute unsoundness. 



In thickening of the Schneiderian membrane, or when 

 abnormal growths occupy the air-cavities of the head, a 

 more or less blowing sound may be heard. 



In some instances, if the obstruction be very great, the 

 sound may become of a whistling character ; this, however, 

 is rare. It may be mistaken for a sound originating in the 



