Zavim, Chapter Four, Mishnah Six
1) If a zav [sat] in one scale of the balance, while food and liquids were in the other scale, [the latter become] unclean.
2) In the case of a corpse, everything remains clean except for a man.
3) This is [an example of] the greater stringency applying to a zav than to a corpse; and there is a greater stringency in the case of a corpse than a zav.
4) For whereas the zav defiles all objects on which he sits or lies upon, so that these likewise convey uncleanness to people and garments, and he conveys to what is above him madaf uncleanness, so that these in turn defile food and liquids.
a) Whereas in the case of a zav no such uncleanness is conveyed.
5) Greater stringency is also found in the case of a corpse, since it can convey uncleanness by overshadowing, and it defiles seven days defilement, whereas in the case of a zav no such uncleanness is conveyed.
Section one: The food or liquids that are on the other side of the scale are lifted up by the weight of the zav. However, they do not have midras impurity, even if they are heavy enough to lift up the (lightweight) zav because midras impurity is only conveyed to objects that are designed to be sat or laid upon. Food and liquid are never susceptible to midras impurity. However, they are impure with first degree impurity, which is lighter than midras impurity.
Section two: The mishnah now begins to compare impurity conveyed by a dead body with the impurity conveyed by a zav. When a dead body is on one side of a balance and something else is on the other side, whatever is on the other side is not defiled because a dead body does not defile by sitting, laying or shifting without contact.
Section three: This is the general statement that sums up this mishnahsometimes the rules are stricter for a zav and sometimes they are stricter for a corpse. This is typical of the Mishnahit loves to compare laws governing different yet similar cases.
Section four: There are two types of uncleanness conveyed by a zav that are not conveyed by a corpse. The first is that a zav conveys uncleanness by sitting or lying on things, such that those items now convey uncleanness even to people and clothing. Furthermore, a zav defiles things that are placed on top of him even if he doesnt touch them. This impurity is called “madaf” and it probably comes from the word for “shelf”madafin Hebrew. This impurity is relatively light for these items defile other food and liquids but they wouldn’t defile clothing and people. Again, a dead body wouldn’t defile in this way.
Section five: A dead body does defile by overhanging (an ohel). We learned about this extensively in Tractate Ohalot. This means that if something hangs over both a corpse and a clean object the impurity of the corpse goes to the clean object. A zav doesn’t defile in this way.