Middle-ear effusions have been produced following eustachian tube obstruction in guinea pigs. This was achieved by plugging the pharyngeal orifice of the tube by an atraumatic lateral transpalatal incision. General anaesthesia was used throughout the entire procedure. The presence of fluid in the middle-ear cavity was determined by observing:
(a) The appearance of pallor of the drum.
(b) Retraction of the tympanic membrance.
(c) Cloudiness of the tympanic bullae on radiographs obtained at weekly intervals, confirmed by:
(d) Subsequent myringotomy.
Serial smears of the induced effusions showed an absence of chronic inflammatory cells except in the case of one animal which developed bacterial otitis media. The presence of secretory cells was demonstrated in the actual epithelial layer and lamina propria but no discrete glands were found. Squamous metaplasia of the lining of the middle-ear cleft was noted. The fluid from the tympanic cavity appeared watery, faintly turbid and non-mucoid, and resembled the serious type of effusion found in man.