=Lesions.= The only lesions consist in very active inflammation of the mucous membrane of the sinus, which appears excessively hypertrophied, and in the existence of larvæ. These develop in the midst of a magma of purulent, fœtid discharge. The number of parasites usually ranges from two to twenty, although Zürn declares that he has found as many as eighty in one subject. =Treatment.= Many precautions have been suggested for preventing infestation. Many are impossible or difficult to carry out in current practice, even the soaking of the nostrils in empyreumatic oil, and the majority are useless. The only suggestion to which we attribute any importance consists in trying to prevent the perfect insects from obtaining a lodgment in cavities in the walls or roofs of sheep-sheds. The really efficacious modes of treatment are also few in number, for the larvæ are so firmly lodged in the mucous membrane of the sinuses that they can only be detached after these have been trephined. The use of nasal injections, embrocations and powders, with the object of making the animal sneeze, are ineffectual. Trepanation should not be performed until it is quite clear that the flock is badly infested, and when serious symptoms appear to threaten the lives of some of the animals. The operation, although very simple, requires care on account of the thinness of the bones. The anatomical directions are the middle line of the head, and a transverse line uniting the upper margin of the two orbits. The orifices are made in the two lower angles produced by the intersection of these lines (Fig. 169). It is then easy to remove with the fingers or forceps the larvæ situated immediately below the point of trepanation, and afterwards to wash out thoroughly the cavities of the sinuses. If some lie at points which cannot be directly reached, they can be killed by injecting a little benzine and water. This proceeding is quite safe. CHAPTER III. LARYNX, TRACHEA AND BRONCHI. LARYNGITIS. Laryngeal diseases are common, but are usually only the local expression of some grave general infection, such as foot-and-mouth disease, gangrenous coryza, or tuberculosis. Pathological conditions such as these can be disregarded for the moment, as they will receive attention under special heads. The two current forms of laryngeal disease are acute laryngitis and stridulous laryngitis. ACUTE LARYNGITIS. Acute laryngitis, like simple coryza, of which it is often only an accompaniment, is caused by chill, by irritant vapours, by smoke, etc., or by external traumatic causes.