 A second bird would then be burnt on the altar as a "whole sacrifice", completely immolated by fire.According to 19th century textual scholars these rules originate from two different layers in the priestly source, thought by scholars to be one of the source texts of the Torah; the priestly code within the priestly source is believed to be a series of additions to the text, from Aaronid editors, over a long period.The earlier source is thought to be the one referring to the flesh being consumed by the priests, the latter part of Leviticus 6 falls into this source, while the later source, which Leviticus 4 falls within, reflects a development where the flesh from sin offerings was seen as insufficiently holy and thus needing to be disposed of elsewhere.