If a vessel arrives in the said port of Chittagong having on board any person suffering from the disease of small-pox, the said Health Officer may, if he deem it expedient in order to prevent the risk of the contagion of small-pox being conveyed into the town or suburbs of Chittagong, require any unprotected person on board such vessel to submit himself forthwith to be vaccinated; and every such person shall, before leaving the vessel, submit himself to the said Health Officer, or any person duly authorized to act in this behalf, for vaccination: Provided that nothing herein contained shall apply to any vessel belonging to, or in the service of, the Government, or to any vessel belonging to any foreign Prince or State.