Quarantine (kwăr'an-tēn' ), ("a period of forty days"), is a forced abstinence from communication with the shore which ships are compelled to undergo when they are last from some port or country where certain diseases held to be infectious, as yellow fever, plague or cholera, are or have been raging. Where a quarantine is established, it is a punishable offense for any person in the suspected ship to come on shore or for anyone to disembark any merchandise or goods, except at lazarettos, which are establishments provided for the reception of goods or passengers or crew, and where such purifying processes as the sanitary science of the time prescribes are applied. Until a ship is discharged from quarantine, she displays a yellow flag at her masthead if she has a clean bill of health, a yellow flag with a black spot if not clean; at night a white light is shown at the same place. The permit to hold intercourse after performing quarantine is called pratique. Quarantine is not of necessity limited to a sea-frontier; it is enforced at the frontiers between adjacent states, and by cities and towns on houses in which are cases of infectious diseases.