Meilah, Chapter 4, Mishnah 5. The later mishnayot of this chapter are built around a single theme: when do separate items join together, mitztarefin, to make up a required measure? Our mishnah leaves the subject of me'ilah proper and gathers a list of measures from across the Torah, in each of which the amount may be reached by adding one food to another rather than by a single item alone. It begins with foods and ends with liquids.
Tum'at hagviyah: the decree of the chachamim
An introduction is needed before the words of the mishnah. Mide'oraita, on the Torah level, a person does not contract tum'ah by eating food that is itself tamei. Food conveys tum'ah to other food, but not to the body of the one who eats it. The chachamim, however, instituted a decree: one who eats tamei food in the volume of a chatzi pras becomes tamei in his own body and is disqualified from eating terumah until he immerses in a mikveh. This status is known as tum'at hagviyah, tum'ah of the body.
The mishnah begins: "Kol ha'ochalin mitztarefin" - every type of food joins together with every other, "lifsol et hagviyah bechachatzi pras" - to render the body unfit with half a pras. Since a whole loaf divides into two perasim, a chatzi pras works out to a quarter of a loaf. The novelty here is that the eater is not required to swallow that quarter loaf from a single item. A bite of this tamei food and a bit of that one, once they total a chatzi pras between them, leave his body tamei and terumah closed to him.
The measure of two meals for an eruv
The measure of two meals for an eruv
"Bimzon shtei se'udot la'eruv" - foods join together as well toward the two meals' worth of food used for an eruv techumin. The background: once the holy day begins, whether Shabbat or Yom Tov, one may not travel farther than two thousand amot from his mekom shevitah, the spot where his residence for that day is fixed, ordinarily the city he is in when the day arrives. Those two thousand amot measured from the city's edge form his techum.
A person who must travel toward a particular side can move that boundary. While it is still erev Shabbat he places food somewhere within two thousand amot of himself, and that deposit fixes his dwelling for the day at that location. His two thousand amot are then measured afresh from there in all directions, so he gains ground on the side he needs and forfeits the same distance on the opposite side.
What quantity of food does this require? The equivalent of two meals, meaning two perasim, which together make one loaf, estimated by some at six eggs and by others at eight. The mishnah teaches that this quantity may be assembled from more than one kind of food. Several different items may be set down together, and once they come to two meals' worth, the eruv takes effect and the mekom shevitah is established.
"Ukheveitzah letamei tum'at ochalin" - and foods combine to reach the volume of an egg for the tum'ah of food. We learn that tamei food does not pass its tum'ah onward unless there is at least the volume of an egg. Here too, the mishnah teaches that a mixture of tamei foods may be added together to reach that shiur.
A dried fig for carrying on Shabbat
A dried fig for carrying on Shabbat
"Kegrogeret lehotza'at Shabbat" - foods join together to reach a grogeret, the size of a dried fig, which is the shiur for the melachah of carrying on Shabbat. Someone who transports food from a reshut harabim into a reshut hayachid has desecrated Shabbat only when what he moved amounts to a grogeret, and several foods carried at once are added together toward that amount.
A large date on Yom Kippur
"Vekhakhotevet beYom haKippurim" - foods join together to reach a koteret, the size of a large date, which is the shiur of eating that brings liability on Yom Kippur. Wherever the Torah speaks of eating, the standard amount that obligates a person is a kezayit. On this day the figure is bigger: a koteret, equal to two kezaytot.
The source of the difference is the language of the pasuk. Concerning Yom Kippur the Torah does not phrase the prohibition as eating at all; it instructs "ve'initem et nafshoteichem", that we afflict ourselves. Chazal explained that a date-sized portion is precisely what starts to quiet a person's hunger, at which point he has left the condition of affliction. A kezayit does not calm him, and he is still afflicted after swallowing it. Our mishnah adds that an assortment of foods may be counted together until they reach a koteret, and whoever ate them bears liability.
The mishnah now turns to beverages: "Kol hamashkin mitztarefin" - all liquids combine, for two halachot.
All liquids combine
The mishnah now moves to drink: "Kol hamashkin mitztarefin" - all liquids combine, and this applies to two halachot.
"Lifsol et hagviyah birevi'it" - the body is rendered unfit by a revi'it. This corresponds to the rabbinic decree with which the mishnah opened, except that the medium is beverage rather than solid food. Whoever swallows a revi'it of tamei liquids, a quarter of a log, something close to three ounces in our terms, becomes tamei in his body and is barred from terumah. Assorted liquids drunk together are counted toward that revi'it.