51Eiruvin 7/7-10

(7) If the [quantity of] food [required for the shituf] becomes lessened, he may [himself] add [to it], and give [the other residents] rights [to this addition], and he need not inform [them]; if [new residents of the courtyard] were added to [the previous ones], he may [himself] add [sufficient food to make up the quantity required], and give them rights [to this addition], and he must inform [them].

(8) How much is [the] required quantity [of food to make a shituf]? When they [the residents] are numerous, nourishment [that is sufficient] for [one person eating] two meals [is sufficient] for all of them; when they are few, the size of a dried fig - [which is also the quantity of food prohibited] to carry out on Shabbat - for each and every one of them.

(9) Rabbi Yose said, "To what does this [preceding law] apply? To the beginning of the eruv [when it is first made]; but to remnants of the eruv [later when some of it has been lessened], any quantity [is sufficient]." And the Rabbis did not say to make an eruv for [several] courtyards [where it is already subsumed by a shituf], except so that the children not forget [the concept of an eruv].

(10) We may use all [food and drink] to make an eruv or a shituf, except for water and except for salt - these are the words of Rabbi Eliezer. Rabbi Yehoshua says, "[Nothing but] a [whole] loaf of bread is [considered an] eruv. Even if one bakes a [whole] se'ah [a specific unit of volume of flour] but it is a portion [and not a whole loaf], we may not make an eruv with it; [whereas] a [small] loaf made from [flour bought with] an issar [a specific unit of money], and it is whole, we may make an eruv with it."