There is some evidence that arsenic has a prophylactic effect.
The planting of eucalyptus trees is out of favour at present, but it appears to have been successful in Portugal, not from any prophylactic virtues in the plant, but through the great absorption of moisture by its deep roots, which tends to dry the subsoil.
Red-spiderall these and similar procedures timed to ~catch the pest at a vulnerable stage are intelligent and profitable prophylactic measures, as has been repeatedly shown.
Medicated soaps for external use are only employed in cases of skin ailments, as prophylactic washes and as disinfectant soaps.
The Indians have a habit of consuming a yellowish edible earth containing sulphur; on pilgrimages they obtain images moulded of this earth at the shrines they visit, and eat the images as a prophylactic against disease.