Midrash su Levitico 7:19

1) (Vayikra 7:19) ("And the flesh (of consecrated peace-offerings) that shall touch anything that is tamei shall not be eaten; it shall be burned with fire. And the flesh — everyone that is clean may eat the flesh.") I might think one who is tamei makes consecrated flesh tamei by carrying it, and that it follows a fortiori, viz.: Now if the ashes of purification (of the red heifer), which a tvul yom (one who immersed in the daytime) does not make tamei by touch, makes it tamei by carrying, then consecrated flesh, which a tvul yom does make tamei by touch, does it not follow that he makes it tamei by carrying it! It is, therefore, (to negate this) written "that shall touch" — he makes it tamei by touch and not by carrying it.

1) R. Yehoshua says: A Pesach offering that came (i.e., that was slaughtered, when the entire congregation [as opposed to an individual] was) in a state of tumah, (this being permitted), and zavim and zavoth (men and women with genital discharges) and niddoth and women who had given birth ate of it, (even though it is forbidden for them to do so) — I might think that they are liable (for tumah-kareth transgression); it is, therefore, written "Everyone that is clean may eat (the) flesh, and the soul that eats flesh, etc." — There is tumah (-kareth) liability only for that which is slaughtered for the clean, but not for that which is slaughtered for the unclean (as in the Pesach instance).

2) This tells me (as not imparting tumah by carrying) only of the lesser forms of tumah (such as that of a sheretz (a creeping thing) or of carrion, which do not make a man tamei). Whence do I derive the same for graver forms of tumah, such as dead-body tumah, and that of cohabiting with a niddah, and all (forms of tumah) which make a man tamei? From "anything that is tamei" (imparts tumah to consecrated flesh) — even one who is lacking atonement (viz. Vayikra 12:7). R. Yossi said: Whence is it derived that fourth-degree tumah invalidates consecrated offerings, and that it follows a fortiori? (From the following:) If one lacking atonement, who is permitted to eat terumah, invalidates consecrated offerings, then third-degree tumah, which does invalidate terumah, does it not follow that it should invalidate offerings (in rendering it fourth-degree tumah)? We derive, then, (the invalidation of) third-degree tumah from the verse ("and the flesh that shall touch, etc."), and of fourth-degree tumah from the argument a fortiori.