When one reads that the cause of hypertension is unknown, a statement fashionable among writers on this topic, it is always hypertension in the greater circulation to which reference is made. The statement means that no single chemical or physicochemical substance has as yet been isolated from the tissues of hypertensive patients that will give rise to a persistent hypertension in animals. The word "cause" has a wide and various meaning. A cause may be ultimate or immediate, a living or an inanimate thing, a deformity or a state of mind, an insult from without or an endogenous upheaval, an event or a fortuitous circumstance, a how and a when and a why.
In the summation of all these factors, one finds that the "cause" of a single disease is hardly known. A harelip is "caused" by a malformation, but the "cause" of the malformation is not known. Tuberculosis is