The city councils shall, from time to time, exempt from the operation of any statute law, conferring on the board of health, jurisdiction of the subject of nuisances such portions of the territory under their jurisdiction, being a rural district or sparse in population, as in their opinion they can do with safety to the health and comfort of the inhabitants thereof, which exemption shall at all times be revocable by the like authority.
53 P.S. § 16604