=Treatment.= Numerous methods of treatment were formerly recommended, such as absolute rest, bleeding, cold affusions, perforation of a horn, section of a horn, etc. None of these is of any value. At first, provided only a certain degree of sensitiveness and simple catarrh without suppuration exist, antiseptic fumigations with tar, carbolic acid, thymol, etc., are useful; but later, when pus has formed, they are useless. At this period the only rational and efficacious treatment consists in trepanation. In unilateral collections three openings are necessary. The first is an opening into the sinus of the horn core. It is made ⅜ to ¾ of an inch above the horn-secreting band of the horn. It must not be forgotten, however, in planning such an opening that the sinus of the horn core only exists in a rudimentary condition in young animals, and that it is scarcely possible to trephine the horns before the patient is three years of age. The second opening is made towards the upper part of the frontal sinus about ¾ inch below the horn-secreting ring at the base of the horn and in a line with the axis of the horn core itself. Whatever the animal’s age and however little the sinuses may be developed, this opening is certain to expose the cavity of the frontal sinus. In old animals where the frontal sinus is enormously developed, and where very large depressions exist in the orbital region, a third opening should be made just above a transverse line uniting the upper margins of the two orbits and inside the suborbital suture. These openings having been made, treatment consists—firstly, in completely washing out the cavity with boiled water, cooled to 95° or 100° Fahr.; and, secondly, in injecting antiseptic and astringent solutions so as to check the formation of pus. Among such may be mentioned 3 per cent. carbolic solution, 5 per cent. carbolic glycerine, 2 per cent. solution of iodine in iodide of potassium, etc. Whatever the drugs employed, the cavities should be washed out every day, first with plain sterilised water, and then with antiseptic solutions at the body temperature, since cold solutions often cause inflammation of the mucous membrane of the opposite sinus. PURULENT COLLECTIONS IN THE MAXILLARY SINUS. This disease is much rarer than that of the frontal sinus, and only within the last few years (Ries, 1899) has a really good description been given of it. =The causation= is imperfectly understood. Injuries to the suborbital region and maxillary ridge, caries of the molar teeth, and inflammation occurring during the development of general diseases represent the principal causes. The dominating and characteristic symptom of the presence of pus in the maxillary sinus consists in incessant snorting, accompanied by violent movements of the head and the discharge of purulent or muco-purulent material.