DISEASES OF THE AIR-PASSAGES OF HORSES. 221 
of roaring. Extensively entering the ramifications of the bronchi 
within the lungs, this kind of thickening may materially interfere 
with the changes of the blood by respiration. 
The Mucous Follicles are subject to enlargement forming so 
many circumscribed granular bodies, varying in colour from a dirty 
white to a dark brown, observed on the inner surface of the mem¬ 
brane encompassed by coloured circles; they may be mistaken for 
tubercles, as they exist or take place without thickening of the mu¬ 
cous surface. Softening has been observed in this membrane, and 
ulceration is not of unfrequent occurrence; these solutions are ge¬ 
nerally found in the larynx, but they may take place in any part of 
the trachea or bronchi: they seldom extend deeper than the cellu¬ 
lar tissue attaching the membrane to the parts beneath, and the tis¬ 
sue at the base of the ulcer is generally much thickened. Ulcers in 
the larynx vary both in number and extent; sometimes only one, 
in other instances several, extending over a considerable surface, or 
one of magnitude may invade a considerable portion of the larynx, 
and without doubt produce roaring. This ulcerated condition of the 
larynx is frequently connected with a tuberculous state of the 
lungs; fistulous openings from excavations in the parenchyma 
sometimes are found in the walls of the bronchi, and such commu¬ 
nications rvith the tube undoubtedly, for the most part, are produced 
by pulmonary excavations breaking into them ; but lam of opinion 
ulceration originating in the respiratory mucous surface may, by a 
process of absorption, perforate the bronchial tube from within out¬ 
ward, and give rise to inflammation and suppuration of the substance 
of the lung. 
Mucous Secretion of the Bronchi. —Alterations of this secretion, 
both in quality and quantity, take place in different states and 
stages of inflammation of the mucous membrane. In diseases im¬ 
mediately affecting this tissue, either acute or chronic, the secretion 
of mucus is frequently very much increased : the quantity in some 
instances is so excessive as to destroy the animal by its accumula¬ 
tion, nearly filling up the bronchi, trachea, and larynx, particularly 
in animals in which the vital energies of the frame are much dimi¬ 
nished, and the inflammatory action has assumed a low type; and, 
what is the more remarkable, this excessive secretion is occasion¬ 
ally unaccompanied by any change of the air-passages. It may 
become so adhesive and viscid, cling to the walls of the bronchi, 
and by accumulation so impede the ingress of air, as to produce a 
fatal dyspnoea. The mucous secretion in other instances is changed 
to a puriform fluid, and this even without a trace of ulceration or 
inflammatory blush in any of the bronchial tubes, or apparent al¬ 
teration of structure: nevertheless, this state of secretion is gene- 
VOL. XIll. G g 
