2nd. =Disease of the valves= _of the heart_ or their insufficiency from cardiac dilatation is a common cause of vertigo, and may be recognized by auscultation and by the general symptoms of chronic heart disease. 3d. =Disease of the lungs= interfering with the flow of blood through the right heart and more distantly with the return of blood from the brain. It further effects the brain functions through the circulation of a highly carbonized blood, which fails to maintain the normal functions of the ganglia. 4th. =Disease of the blood vessels=, it may be by emboli washed on from clots in the pulmonary veins or the left heart and arrested in the vessels of the brain; it may be by aneurism of the anterior aorta as reported of a horse (Lustig); it may be by phlebitis and thrombosis of the jugulars; it may be by adjacent tumors pressing on the vessels. 5th. =Gastric Vertigo=, =Abdominal Vertigo=, is a complication of gastric or hepatic disorder with giddiness and unsteady movement. The abdominal disorder may be at once a cause and result of the vertigo and it is not always easy to decide which predominates. The unsteady movements in certain cases of overloaded stomach, in the horse are illustrations of purely abdominal vertigo, while on the other hand in vomiting animals nausea, retching, emesis, and other gastric disorders promptly attend on the primary cerebral disorder. There is also a special tendency to vertigo in the fat, idle, gorged horse and in those with torpor or other disorder of the liver occurring in pampered horses in spring and early summer. 6th. =Optic vertigo= is a reflex disorder, determined in the excitable nerve centres by the visual influence. Thus it has been seen in horses and sheep from the intense glare of the sun’s rays, reflected from a lake or river or from white snow or ice, or even from the glistening inner surface of the blinds. The effect is intensified if the animal has just emerged from a dark stable or a darker mine. The overdraw check may be a factor by reason of its turning the eyes upward and exposing them continuously to the full glare of the sun. The sense of motion conveyed through the eyes contributes to bring on giddiness and a sense of swimming. In man this is notorious, the sense of nausea and vertigo being precipitated by looking at the nearby, moving objects in cabin or on deck, while it may be retarded by directing the eyes to steady distant objects. As dogs, horses and other animals suffer from seasickness, and even railroad sickness, this attendant factor may be logically accepted. The mere limitation of the field of vision, by the use of blinds, and the disappearance in rapid succession of near objects behind this narrow screen probably has an influence similar to the visible motions in the ship between decks, in cases in which these portions of the harness are manifest factors.