These cases are to be distinguished from epilepsy by the absence of any spasmodic contraction, aside from the jerking of the head and rolling of the eyes, and by the fact that consciousness is retained throughout. During the attack the animal may fail to respond to irritation of the nasal mucosa, but this appears to be due to the fact that his whole attention is engaged with a more serious trouble. The duration of an attack is from one to two, or exceptionally five minutes. The form which is represented by jerking of the head and deviation from the direct line of motion may continue so long as exercise is kept up. In the =nasal vertigo= of sheep and dogs, due to parasites, sneezing, and congestion of the mucosa are to be looked for. In the =cerebral parasitic vertigo= of sheep and pigs, the symptoms vary according to the seat of the parasite. These may be blindness, turning in a circle, moving straight ahead regardless of obstacles, jerking upward of the head with nose protruded, hemiplegia, hemianæsthesia, cross hemiplegia, cross hemianæsthesia, and any one of the many forms of paralysis, or exaggerated nervous action. The animal usually turns to the side on which the parasite lies and is paralyzed on the opposite side of the trunk. A peculiarity of these cases is that while the symptoms are continuous, yet there are periodic aggravations which bear no relation to feeding, exertion or excitement, but depend on the protrusion at intervals of the heads of the parasites into the brain substance. If there are several parasites in the brain and they do this at different times the symptoms are liable to vary according to their seat, and the special organ which is irritated. This variability of symptoms is suggestive of parasitism. While turning around in a circle has been already noticed there remains, in certain cerebral forms, the peculiar phenomenon of the animal rotating rapidly on its longitudinal axis. The patient falls on its side and rolls over and over. Among the brain lesions with which it has been experimentally identified are injuries to the _middle peduncles of the cerebellum_, or of the _superoexternal portion of the cerebral peduncles_, or of the _posterior part of the encephalon_, or of different parts of the hemispheres. Cases of vertigo that occur without any appreciable lesion have been named _essential vertigo._ Guibert has attributed some cases to irritation of the lower part of the limbs by contact with the litter but this could only occur in an animal in which the nervous system was in a morbidly excitable condition.