7th. =Aural Vertigo= is determined by irritations of different kinds affecting the external, middle or internal ear. Experimental sections show that this is especially due to injuries of the semicircular canals. If the _horizontal canal_ is divided there are pendulum-like movements of the head alternately to the right and left, also lateral rolling of the eyes. If the _posterior canal_ is cut there is a vertical movement, or nodding of the head and vertical rolling of the eyes. If the _superior vertical canals_ are injured there are pendulum-like vertical movements of the head and the animal tends to fall forward. Injury to the _anterior canal_ causes diagonal rolling of the eyeball. In destruction of _all the canals_ various pendulum-like movements are performed, and standing often becomes impossible. Stimulation of one auditory nerve is followed by rotation of the eye and rotation of the body on its axis toward the injured side. The passage of a galvanic current through the head _between the mastoid processes_, or _from one external auditory meatus to the other_, causes rolling of the eyeballs. _Injection of water violently into a rabbit’s ear_, or of _iced water_ or of a _rhigolene_ jet, causes rolling of the eyes, and rotation of the body toward the side operated on. Dr. Weir Mitchell had a similar experience in his own person. If the injections are repeated a permanent vertiginous condition is induced, and the rabbit or Guinea pig, which has been kept in darkness for a few hours and is then suddenly exposed to sunlight, is unstable on its limbs for a few seconds. Lucæ found that with perforation of the membrana tympani, an _ear air douche_, at 0.1 atmospheres caused abduction of the eyeball, dyplopia, giddiness, sense of darkness, and disturbed respiration. Vulpain found that a 25 per cent. solution of _chloral hydrate dropped into the ear_ of a rabbit caused vertiginous movements. McVey records the case of a music teacher who had intense vertigo induced by the _low bass notes_ of a piano. Crum Brown noticed that if a person with bandaged eyes, is rotated for some time as on a potter’s wheel, he can at first estimate the degree of rotation, but after a time he fails to do so, and the rotation may be stopped, without checking his sense of whirling. The familiar method of subduing an intractable or vicious horse by _running_ him rapidly around _in a very narrow circular course_, or by tying head and tail together and letting him circle around until he staggers or falls, is another manifest example of this aural vertigo. Rabbits and dogs suffering from _acariasis of the external ear_ move around in a circle, or even turn somersaults tending toward the affected side. Trasbot has found larvæ of insects (simulium cinereum?) in the ears of vertiginous horses, which he successfully treated with injection of chloroform. Even hard pellets of wax pressing on the tympanic membrane have been found to give rise to vertigo.