X ‘ J ‘ J TYMPANITES OF THE GUTTURAL POUCH. 
gas in the guttural pouches, which become so dilated as to cause severe 
dyspnoea. A swelling appears in the region of the parotid which is 
lesonant on percussion, and on strong pressure sometimes produces a 
whistling sound in consequence of air escaping from the Eustachian tube. 
It usually occurs in young animals, foals, and affects both guttural 
pouches. If the sac is opened the gases escape, but reaccumulate as 
soon as the opening closes. Reported cases show that tympany may be 
due to either of two causes. 
(1) Atmospheric air enters through the Eustachian tube and gradually 
accumulates in the guttural pouches. This probably occurs during 
deglutition, and is caused by deformities in the tube allowing its opening 
to act as a valve, which admits air but prevents its exit. Even in normal 
subjects, exit of air appears to be difficult. Degive injected air through 
a trochar into the guttural pouch of a dead animal, and noticed that it 
was retained for a long time. Gerlach referred the condition to para¬ 
lysis of the elevator of the soft palate, which he considered should close 
the Eustachian tube, because in one of his cases these muscles seemed 
atrophied on the diseased side. K. Gunther also considered that the 
pouch might become distended in this way. The air which has so 
enteied, according to Gerlach, is unable to return, because the tube 
closes like a valve at its point of entry into the guttural pouch. In¬ 
vestigations in the horse, carried out with the pharyngeal speculum, do 
not, however, support this idea. The open end of the Eustachian tube 
can be directly observed with the instrument. Closure by the soft palate 
may certainly occur during swallowing, and entrance of air he caused by 
the soft palate not properly covering the opening of the Eustachian tube. 
The significance of the guttural pouches has been variously interpreted. 
Franck looks on them as safety valves to control the air pressure in the 
middle ear, and prevent excessive tension of the tympanum by alteration of 
pressure. The suggestions that they are involved in voice production, or that 
the respiratory air is warmed during its stay in them, seem improbable. 
Perosino discovered, by experiment, that during expiration the pouches were 
dilated, and that during inspiration they collapsed again. He introduced a tube 
containing alcohol into the pouch through a trochar, and noticed that the fluid 
lose during expiration and fell during inspiration. The phenomenon was 
exaggerated during violent expiration. Perosino therefore considered the 
guttural pouches were intended to moderate the stream of inspiratory air 
during violent exertion. Prince, on the other hand, supports the view first 
suggested by Prange, viz., that the guttural pouches serve to assist movements 
of the head by acting as elastic cushions. Perosino states that, in animals 
suffocated by stopping up the nostrils, the guttural pouches are enormously 
dilated. 
(2) Other published observations ascribe the condition to the develop¬ 
ment of gas during catarrhal disease of the guttural pouch (Bassi, Degive, 
Molier). Cases associated with disease of the mucous membrane and 
