DISEASES OF THE AIR-PASSAGES OF HORSES. 
223 
on one side, whilst those on the other have wasted away and nearly 
vanished; a condition to which roaring has been by some patho¬ 
logists mainly attributed*: in other instances of alteration of the 
muscular tissue are infiltrations of different morbid secretions. 
The Cartilages of the air-passages are frequently diseased ; ul¬ 
ceration is mostly met with in those of the larynx, and generally 
commences in the soft parts covering them. Ossification is very 
common to the thyroid and cricoid ; occasionally the epiglottis is 
thickened and indurated; but this and the arytenoid cartilages are 
rarely, if ever, found ossified. The tracheal rings are sometimes 
ossified and anchylosed, but other changes in them are seldom met 
with. The tubes of the bronchi may become ossified; a brittle 
fragile condition I have many times observed, even in the minutest 
subdivisions of them. 
Alterations of the Cellular Substance, entering into and connect¬ 
ing the several structures of the air-passages, consist of softening, 
by whicli it is more or less destroyed; and thickening and indura¬ 
tion : it is often the seat of congestion and inflammation. By a 
subacute inflammation it is softened and destroyed, and by chronic 
inflammatory action it is also indurated and thickened : it is some¬ 
times infiltrated with serum, and oedematous, by which the mucous 
membrane is distended, lessening the caliber of the glottis, affect¬ 
ing seriously the action of the muscles, the form and movements 
of the epiglottis, together with the rima glottidis, impeding the 
ingress and egress of air in a greater or less degree. This state of 
the cellular tissue is generally consecutive of the inflammation of 
the mucous surface, or the result of chronic disease of the larynx. 
Cases present themselves in which the intensity is of a very low 
grade ; and others, in which the inflammatory action is exceedingly 
acute and rapid. I have many times seen the caliber of the glottis 
so diminished in the horse, and, but for tracheotomy, fatal dyspnoea 
must have ensued. Pus is occasionally found infiltrating this tissue 
more or less in extent, or in the state of small abscesses; and it is 
sometimes the seat of tuberculous matter : different kinds of tumours 
occasionally occupy the cellular tissue of the larynx and parts ad¬ 
jacent, and either by pressing on the nerves, or the movements of 
glottis, produce similar effects to those resulting from disease of its 
walls. 
Change of Caliber in the Air-passages. —The alterations enu¬ 
merated above as occurring in the several tissues, change in a 
remarkable manner the size of the air-passages. A diminution of 
capacity is occasioned by thickening of the mucous membrane; 
infiltration of the sub-mucous cellular tissue in or about the larynx; 
* In some future paper I intend to offer a few remarks on the subject of 
roaring. 
