Midrash su Levitico 15:10

1) (Vayikra 15:10) ("And whoever touches anything that is beneath him shall be unclean until the evening, and one who carries them shall wash his clothes and bathe in water, and he shall be unclean until the evening.") "And whoever touches anything that is beneath him": beneath the zav (i.e., if one touches the saddle). I might think (that the meaning is) "beneath it," the saddle. It follows a fortiori (that this cannot be said), for if the zav (himself), the stringent (instance), does not confer tumah upon vessels requiring rinsing (to release them from tumah) except by touch (of the zav himself), then the saddle, the less stringent (instance), how much more so does it not confer tumah upon vessels requiring rinsing, except by touch. How, then, am I to understand "And whoever touches anything that is tachtav? As meaning "beneath him," the zav, (i.e., if one touches the saddle).

2) "and one who carries them": What is the intent of this? I might think that only merkav alone confers tumah by being carried. Whence do I derive the same for mishkav and moshav? (But a verse is not necessary for this.) I know it a fortiori, viz.: It merkav, which does not confer tumah upon garments by being touched, does confer tumah upon garments by being carried, then mishkav and moshav, which do confer tumah upon garments by being touched, how much more so do they do so by being carried! — (No,) this is refuted by the upper board and the side board of a coffin (viz. Bamidbar 19:16), which do confer tumah upon garments by being touched, but which do not do so by being carried.

3) Do not wonder, then, if mishkav and moshav do not confer tumah by being carried even though they do confer tumah by being touched. It must, therefore, be written "and one who carries them," to include mishkav and moshav.