The gadfly of the sheep (_œstrus ovus_), allied to the gadfly of cattle (_œstrus bovinus_), is the plague of the flocks in August and September, as the other is of the herds; but it chooses a different place for the deposition of its eggs. The locality selected is the alœ, or flaps of the nostrils of the healthiest and finest sheep of the flock, while they are sleeping in the pasture. There the eggs, warm and moist, are speedily hatched. Thence the larvæ ascending the nasal cavity, travel to the frontal sinuses, where they remain, living on the mucous secreted there, until their metamorphosis. During their course upward they irritate the delicate membrane with their hooklets; and when then return from their hiding place for expulsion from the nostrils in the following spring, the irritation is renewed. The irritation, and consequent inflammation, pain and sense of dizziness, drive the sheep to distraction. The animal stamps, throws up his head, sneezes violently, and repeats the expulsive effort until the larvæ come away with a large quantity of mucous. The number of larvæ is usually not large; but when it is considerable, the inflammation may turn to gangrene and cause death. After expulsion, the larvæ bury themselves in the ground, assume the pupa state, in two or three months come out as gadflies, and again torment the sheep. The treatment of this affection by means of powders blown up the nostrils, is often as irritating and injurious as the presence of the larvæ. I.J., should be given internally. The inhalation of fumes of sulphur will cause sneezing; and if the larvæ be not already dead, they should be destroyed. Fly Sheep that are wounded by butting each other, or any other cause, that have sores, that are dirty about the tail and quarters, are attacked by a large blow-fly, which deposits its eggs in the wound or putrescence. It is during the summer, in sultry weather and after rain that the fly is the most troublesome. After a while the eggs are hatched, and the maggots burrow in the flesh of the animal. Their presence is indicated by local swelling, pain and dejection, and ultimate debility of the animal. If the maggots are not promptly destroyed and the wound kept clean, suppuration, deep ulcerations and death ensue. Mercurial applications poison the sheep as well as the maggots. The best treatment is to remove the maggots and keep the wounds clean, and apply HUMPHREYS’ VETERINARY OIL or a 2% lysol solution. CHAPTER VII.—PART III. SCAB, TICKS AND DIPPING Sheep are infested with two kinds of external parasites. (1) The sheep tick, which is a wingless fly, less than a quarter of an inch long, and, (2) the acarus which causes scab; of these there are several different species, but since the symptoms are much the same and the treatment exactly the same in all cases it is hardly worth while to differentiate between them.