And be it further enacted, That, in all that territory ceded by France to the United States, under the name of Louisiana, which lies north of thirty-six degrees and thirty minutes north latitude, excepting only such part thereof as is included within the limits of the State contemplated by this act, slavery and involuntary servitude, otherwise than in the punishment of crimes whereof the party shall have been duly convicted, shall be and is hereby forever prohibited: Provided always, That any person escaping into the same, from whom labor or service is lawfully claimed in any State or Territory of the United States, such fugitive may be lawfully reclaimed, and conveyed to the person claiming his or her labor or service, as aforesaid.