E.P. Sanders has written two major studies of this material: one from the perspective of Jewish law as it appears in New Testament sources, Jewish Law from Jesus to the Mishnah, esp. pp. 29–57 (purity, tithes, and temple tax) and pp. 258–271 (purity); the other using early Christian materials to supplement his discussion of Law and practice in Jewish sources, Judaism: Practice and Belief 63 B.C.E.-66 C.E. (Philadelphia: Trinity Press, 1992). For an earlier reconstruction from the Jewish material itself, see Jacob Neusner, The Idea of Purity in Ancient Judaism (Leiden: E.J. Brill, 1973), with a response by Mary Douglas.