(155.) _Inflammation produced by Insects in the Air Passages._ Much annoyance is caused to the sheep by the presence of animals in the air passages. The _OEstrus ovis_ deposits its eggs on the margin of the nostril in autumn; these are soon hatched, and the larvæ immediately find their way up the interior of the nose, till they arrive at the frontal sinus, a cavity situated between the layers of the frontal bone, and of considerable size in the sheep. Here they remain till the following spring, when they quit their hold, become winged insects, and enter upon the career of torment so ably gone through by their predecessors. The _Pentastoma_, an animal supposed at one time only to exist in the frontal sinus and lungs, and on the surface of the liver, of the dog, wolf, and horse, as well as in some reptiles, has been discovered by an able naturalist, my friend Mr Rhind of Edinburgh, in the frontal sinus of the sheep. It spends its whole existence there, and is distinguished from other entozoa by having the mouth between two pores on each side, through which a spicular process comes out. Figure 3, Plate VII. is taken from a drawing kindly furnished by Mr Rhind. (156.) _Removal of Insects from the Nostril._ The _OEstrus ovis_ occasions much distress to the sheep at the moment of depositing its eggs within the nostril. The animal on feeling the movements of the fly, rubs its nose against the ground, or, carrying it low, darts off at a rapid pace, vainly endeavouring to escape from its tormentor. During this period, a thin limpid fluid distils from the nostrils, leading a careless observer to confound the symptoms with those which accompany Coryza. In general the irritation is now terminated, as, while in the larvæ state, the insects are incapable of offensive measures. If they are clustered in considerable numbers in the frontal sinuses, they will doubtless lead to great suffering, parallel to what is recorded to have followed the nestling of insects in the same situation in the human being; and it is, therefore, advisable, when the cause of sturdy (paragraph 169) is in any way doubtful, first to apply those substances to the nostril, which are calculated to destroy both these larvæ and the _pentastoma_, should they happen to be there. Tobacco smoke is the only available remedy, and a very good one, being easily brought in contact with the worms, and, when properly administered, certain in its effects. One person secures the sheep holding the head in a convenient position, while another, having half filled a pipe with tobacco, and kindled it in the usual manner, places one or two folds of a handkerchief over the opening of the bowl, then passes the tube a good way up the nostril, applies his mouth to the covered bowl, and blows vigorously through the napkin. When this has continued for a few seconds, the pipe is withdrawn, and the operation repeated on the other nostril.