There is some evidence that arsenic has a prophylactic effect.
The Metternich stela (XXXth Dynasty), the finest example of a class of prophylactic stelae generally known by the name of "Horus on the crocodiles," is inscribed with a long text relating the adventures of Isis and Horus in the marshes of the Delta.
Both it and the aromatic solution are powerful intestinal astringents, and are therefore useful in diarrhoea of a serious type, being strongly recommended both as a prophylactic and as a treatment during epidemics of Asiatic cholera.
Small doses of the aromatic acid also serve as a prophylactic to those artisans who work in lead and as a treatment in lead poisoning in order to form an insoluble sulphate of lead.
The supreme value of quinine is as a specific antidote to malaria, against which it also possesses a powerful prophylactic action.