In 1787, Congress passed an ordinance for the government of the territory northwest of the river Ohio which had been ceded to the United States by Virginia. The sixth article of this ordinance prohibited slavery in said territory. Inasmuch as the rights of persons and property had been guaranteed by treaties when this region had passed from France to Great Britain and later to the United States, this article was generally construed as meaning that no more slaves should be introduced, and that all children born after the passage of the ordinance should be free, but that slaves held there prior to 1787 should continue in bondage. Immigration was mainly from the Southern States. Some of the immigrants brought slaves with them, and the territorial legislature passed an act in 1812 authorizing the relation of master and slave under other names. It declared that it should be lawful for owners of negroes above fifteen years of age to take them before the clerk of the court of common pleas, and if a negro should agree to serve for a specified term of years, the clerk should record him or her as an "indentured servant." If the negro was under the age of fifteen, the owner might hold him without an agreement till the age of thirty-five if male, or thirty-two if female. Children born of negroes owing service by indenture should serve till the age of thirty if male, and till twenty-eight if female. This was a plain violation of the Ordinance of 1787 and was a glaring fraud in other respects. The negroes generally did not understand what they were agreeing to, and in cases where they did not agree the probable alternative was a sale to somebody in an adjoining slave state, so that they really had no choice. The state constitution, adopted in 1818, prohibited slavery, but recognized the indenture system by providing that male children born of indentured servants should be free at the age of twenty-one and females at the age of eighteen. The upshot of the matter was that there was just enough of the virus of slavery left to keep the caldron bubbling there for two generations after 1787, although the Congress of the Confederation supposed that they had then made an end of it.