Section 1. When implied entailments barred
In all cases of implied entailments, twenty-one years' actual possession of the premises and treatment of the estate as a fee simple, by the donee and those claiming through or under him by grant in form of conveyance, in fee simple or by judicial sale, shall be held a complete bar of such implied or supposed entailment: Provided, That such bar shall not operate against any inheritance that may have vested in any heir in tail before the passage of this act. (1874, May 21, P.L. 221, sec. 1.)