At the beginning of these attacks of snorting, which are produced by the reflux of pus from the sinus towards the nasal cavities, the respiration becomes snoring and rapid, and the animal makes sniffing movements as though the nasal cavities were partially obstructed. After these crises, the respiration again becomes silent. Contrary to what has been observed in purulent collections in the frontal sinus, the discharge is unilateral, reddish yellow in colour, viscous in consistence, and is accompanied by clots of a gelatinous material or even of blood. During the attacks of snorting, the discharge resembles that of croupal or pseudo-membranous bronchitis, but the material discharged is not moulded on the internal shape of the bronchi. The masses of discharge are irregular in form, and appear as though made up of fibrous tissue matted together. Attention having been attracted by the discharge, exploration of the trachea and chest reveals nothing; on an examination of the sinuses, however, palpation and percussion betray a certain amount of sensitiveness, together with partial or complete dulness, and the lesion is discovered. =Diagnosis.= Confusion between pus formation in the maxillary and frontal sinuses can be avoided by careful examination. =Prognosis.= The prognosis is not very grave; the animals maintain their appetite, but become thinner, and the condition shows no tendency to spontaneous cure. =Treatment.= The only rational treatment consists in trephining, an operation practised immediately above the maxillary tuberosity and over the lowest part of the sinus (Fig. 164). This opening allows the cavity to be washed out and the sinus drained. Antiseptic treatment exactly resembles that of purulent collections in the frontal sinus. Injections of astringents, dilute carbolic acid and iodine solutions, etc., are recommended. ŒSTRUS LARVÆ IN THE FACIAL SINUSES OF SHEEP. (FALSE STURDY.) =Causation.= This disease of sheep, which sometimes produces vertigo resembling that shown in gid or sturdy, is produced by the growth of larvæ of _Œstrus ovis_ in the frontal sinuses. The œstrus of the sheep assumes perfect insect form during the fine days of summer from July to September. The females swarm around the flocks and attempt to alight on the animal’s head close to the nostrils, where they deposit their eggs or larvæ. The larvæ crawl into the nostrils, thence into the nasal cavities, the meatus, and finally the sinuses, where they become fixed. In these sinuses they undergo complete development, increasing from a length of about ⅒ inch to from ¾ to 1 inch before their transformation into the nymph and perfect insect. They remain in the sinus for eight to ten months. When numerous and well developed they may fill the whole of the cavity.