The explanation of cases of aural vertigo, has been sought in the physiological action of the endolymph and perilymph on the end filaments of the nerve in the membranous labyrinth, the turning of the head from one side to the other having the effect of changing the pressure in different parts and establishing currents by which the change of position is recognized; on the other hand any injury to the canals, by disturbing the pressure of the perilymph and interfering with the relative position of the canals, and the direction and force of the currents of the endolymph and perilymph, destroys all proper sense of balance. The rotation of the subject as on a wheel or in turning in a narrow circle, is held to cause circular currents in and around the membranous labyrinth which temporarily destroy all sense of equilibrium. Seasickness and railroad sickness are doubtless in part due to the swaying motions causing disturbance in the canals. The intimate relation between the root of the auditory nerve and that of the vagus in the medulla, may serve to explain the mutual interdependence of derangement of the stomach and liver on the one hand and the occurrence of vertigo on the other. Again the relation of vertigo to visual troubles, both as to cause and effect, has been attributed to the close relations of the ganglia presiding over the 3d, 4th, 5th and 6th nerves and those of the nerve of hearing. There is a degree of deafness in nearly all cases of aural vertigo, a circumstance which may be utilized in the diagnosis of such cases, the presence of disease of the guttural pouch, or Eustachian tube, and evidence of deafness on one side rather than the other, may be taken as corroborative evidence of the affection. On the other hand James shows that the stone deaf are much less subject to both seasickness and vertigo than those that hear. The disorder that leads to vertigo implies a retention of a measure of the normal function of the internal ear, and therefore of hearing, whereas the disease that has caused complete destruction of the internal ear and consequent loss of hearing has equally destroyed the function of the labyrinth in maintaining a sense of balance, and has obviated the aural sensations of equilibrium and loss of balance. 8th. =Cerebral Vertigo= may be associated with derangement of the circulation, or disease in the brain or its meninges. Anæmias and congestions resulting from disease or impaired function of heart, lungs, arteries or veins have been already noticed. It remains to note the presence of cholesteatomata and other tumors, and of parasites (cysticercus cellulosa in pig; cœnurus cerebralis in sheep) in the encephalon, and of injuries from concussion, degeneration and softening of the brain substance.