VERTIGO, or giddiness. is a peculiar sensation depending probably on some disturbance of the circulation in the brain. It need nut be described, for whoever has not felt it may do so at once by terming round a few times rapidly. The nature of the change pro duced in the brain by the numerous causes of giddiness is altogether unknown ; probably the sensation may be the result of several differ ent conditions, for it ensues alike when the pressure of the blood upon the brain is diminished by bleeding and when it is increased in plethora, or what is called determination of blood to the head : it is a sign too as well of deficiency of food as of repletion ; and of the varioua continued movements by which the steady flow of blood through the brain may be disturbed, though the rotatory motion is the most general cause of giddiness, yet the movement of the head backwards and forwards or from side to side will produce it as effectu ally. and the vertical movement, such as is endured in the pitching of
a ship, more certainly still. At present therefore it must be concluded that whatever disturbs the movement or the pressure of the blood within the brain may produce giddiness; and that in some cases it occurs without any cause of this kind, as a sympathetic or purely subjective eensation, dependant on the state of the substance of the brain itself.
Aa a sign of disease vertigo by itself indicates very little. No judg ment can be formed from it except by taking it in connection with the other characters of the affection of which it is a part, and these will generally be sufficiently indicative. Its most common cause is some disturbance of the digestive organs, and it may be safely treated in that view, except in those who are prone to apoplexy or other cere bral disease, in whom it must be always regarded with fear.