It may be permissible to consider vertigo under the general head of inco-ordination, because it usually finds a motor expression, either actual or subjective. Subjective vertigo consists in a sense of whirling or horizontal movement which is clearly referred to the brain by the patient. The {50} sensation is variously expressed: in some the head seems to whirl around; in others external objects seem to whirl about the patient horizontally or vertically; in others still there is a sensation of falling in a given direction or of dropping into a hole. Dizziness is a minor degree of subjective motion conjoined with more or less confusion and other paræsthesiæ in the head. Static vertigo is that form in which there is actual loss of equilibrium, or falling. It is observed more especially in diseases of the internal auditory apparatus, and it may be produced artificially by galvanization of the brain. If the electrodes are placed exactly on the median line, and the current passed fronto-caudad through the brain, no loss of equilibrium or vertigo is produced. If, however, the current is passed transversely through the brain, there is produced at the moment of the closure and opening of the circuit a distinct tendency to fall or an actual fall to one side: in closing the current the fall is always away from the negative pole or cathode. The greatest amount of disturbance is produced when the electrodes are placed on the mastoid processes or near them. Whether the disturbance of equilibrium is caused by a change in electrotonus in the hemispheres, or by a change in the vascular supply of the hemispheres (in one anæmia, in the other relative hyperæmia), is uncertain. A third explanation is equally plausible—viz. that the vertigo is caused by unequal excitation of the internal acoustic organs and the two halves of the cerebellum. This view would be supported by the fact that in animals and man a lesion of the acoustic nerve and of the processus ad pontem on one side produces strong rotary movements about the long axis of the body. ABNORMAL REFLEX MOVEMENTS.—Some reference has already been made to absence or exaggeration of reflexes in the preceding paragraphs, but the importance of these symptoms demands that they should be separately considered.