344 DISEASES OF THE AIR-PASSAGES OF HORSES. 
first stage and in an acute form of the disease, produce swelling and 
tumefaction of the membrane, and consequently lessen the capacity 
of the air-tubes, and give rise to a modification or change of cha¬ 
racter of the respiratory sound in them. Hence auscultation gives, 
at the commencement, the dry bronchial rhoncus—generally a deep 
tone, resembling the bowing of some low note of a stringed instru¬ 
ment—and sometimes of a sibilant or whistling sound, more espe¬ 
cially when seated in the large bronchi. These sounds exist in the 
early stage, previous to expectoration of mucus, and are owing to 
the state of the membrane and sub-tissue. The difficult respiration 
at this period is also produced by the same cause. 
To the above sounds the mucous rale succeeds, and becomes pre¬ 
dominant as the secretion of the bronchi advances. The bubbles 
of mucus are considerable, and interrupted when the large tubes are 
affected by inflammation. 
When the small bronchi are the seat of inflammation, the mucous 
rattle is sharper, and may be heard constantly. The mucous secre¬ 
tion becomes thickened and opaque as the disease advances, and the 
rale more uneven. The respiratory murmur disappears in some 
portion of the lung, and the sibilous click is substituted. Obstruc¬ 
tion, partial or entire, of some of the tubes, from accumulation of 
viscid mucus, is a cause of this change in the sound. It is but of 
temporary existence, taking place first in one part of the lung, and 
retiring, to appear in another. The difficult respiration of this stage 
of the disease is plainly illustrated by the condition of the bron¬ 
chial tubes. 
In bronchitis the cough is deep, painful, loose, diffused, and oc¬ 
curring in paroxysms, accompanied by febrile disturbance : laryngi¬ 
tis produces a cough shrill or grunting, and suffocating; pneumo¬ 
nia, one deep in the chest, full,'hard, and frequent; and in pleurisy 
it is short, dry, hard, occasionally slight, but always suppressed and 
painful. 
In acute bronchitis the breathing is hurried, difficult, and wheez¬ 
ing ; in pneumonia less so, and rarely attended by the bronchial 
rale. 
The expectoration in bronchitis after the third day is gene¬ 
rally considerable, and nasal flux even from the commencement in 
some cases; while in laryngitis, pneumonia, and pleurisy, it is thin, 
sparing, or altogether wanting. The pain in bronchitis is less 
acute. The animal never looks back to his sides, as in pneumonia, 
and more especially in pleurisy. 
In pneumonia the pulse is quick, undeveloped, and oppressed ; 
in pleuritis, full, less frequent than in pneumonia, and sometimes 
wiry; whilst in bronchitis it is 70 or more, small, soft, and mode¬ 
rately developed. 
