Zavim, Chapter 2, Mishnah 4. Having dealt with when a man becomes a zav, the mishnah now turns to the reach of his tumah. A zav does not convey tumah only by touch. He also imparts a severe tumah to whatever he lies or sits upon, and that object in turn becomes a source of tumah for others. Our mishnah counts the ways in which each of these two transfers takes place.
The zav and the mishkav: five ways
"Hazav metamei es hamishkav b'chamishah derachim l'tamei adam l'tamei begadim": the zav renders a mishkav, a couch or seat, impure in five ways, and that mishkav then has the power to render a person tamei and to render his garments tamei along with him. The garments are included because the tumah passes to them while the person is still in contact with the source; his clothing and his keilim are drawn in together with him.
The five ways are: "omeid, yosheiv, shocheiv, nitleh, v'nish'an": standing, sitting, lying, being suspended above it, and leaning upon it. Whichever of these five positions the zav takes with respect to the couch or the seat, he renders it an av hatumah, a primary source of tumah. This is what the mishnayos throughout Zavim call a midras hazav.
The mishkav and the person: seven ways
Once the couch or the chair has become a midras hazav, the mishnah continues: "v'hamishkav metamei es ha'adam b'shivah derachim l'tamei begadim." Now the object itself conveys tumah to a person in seven ways, and that person's garments and vessels become tamei as well.
The seven are: "omeid, yosheiv, shocheiv, nitleh, v'nish'an, b'maga u'v'masa." The same five as before, standing, sitting, lying, being suspended over it and leaning on it, with two more added: maga, ordinary touching, and masa, carrying it. The zav's own contact could produce midras only in the five postures of pressure; the object he made tamei, being now an av hatumah in its own right, passes tumah on even by simple touch and even to one who merely carries it.
In every one of these seven ways, the person who came into contact with the midras becomes tamei, his begadim and his other keilim become tamei with him, and all of them must then undergo the process of purification.