Gemara

54a (Mishnah): If calf meat swelled or if meat of an old animal shriveled, we judge them l'Kemos she'Hen (according to their volume).

(Rav (and R. Chiya...)): The text is Kemos she'Hen (according to their current volume).

(Shmuel (and R. Shimon bar Rebbi...)): The text is l'Kemos she'Hen (based on the original volume).

Question (against Shmuel - Beraisa): If calf meat was less than (k'Beitzah, i.e. the volume of an egg) the Shi'ur for Tum'ah, and it swelled to the Shi'ur, it is retroactively Tahor (i.e. regarding Tum'os before it swelled) and Tamei for the future.

Answer: Mid'Rabanan it is Tamei for the future. (Mid'Oraisa, it is Tahor.)

Question (Seifa): The same applies to Pigul and Nosar.

If we follow the current volume mid'Rabanan, we cannot say that Chachamim are Mechayev Kares for (swelled) Pigul or Nosar!

Answer: It means that the same applies to Tum'ah of Pigul and Nosar. The Tum'ah is only mid'Rabanan. The the Beraisa teaches that even so, Chachamim applied another mid'Rabanan stringency to it (to follow the current volume).

Question (against Shmuel - Beraisa): If meat of an old animal was a Shi'ur, and shriveled to less than a Shi'ur, it is retroactively Tamei, and Tahor for the future.

Answer: (Rabah): All agree that if at first there was a Shi'ur and now there is not, (for the future) we follow the present. All agree that if at first there was not a Shi'ur and now there is, we follow the present mid'Rabanan. They argue when there was a Shi'ur, it shriveled to less than a Shi'ur, and then returned to its original size. Shmuel holds that Dichuy applies to Isurim (and Tum'os. Since one was not liable for it when it was shriveled, one will never be liable for it again). Rav holds that Dichuy does not apply to Isurim.

Question (against Shmuel - Mishnah): If k'Beitzah of food, or a k'Zayis of or Neveilah was left in the sun, and it shriveled to less than a Shi'ur, it loses its Tum'ah (i.e. ability to be Metamei). If a k'Zayis of Chelev shriveled to less than a Shi'ur, one who eats it is not liable for Pigul, Nosar or Chelev. If it was left in the rain and returned to its original size, it is again Tamei (or one is liable for eating it).

This shows that Dichuy does not apply to Isurim!

55a Question (against Rav - Beraisa - R. Elazar): R. Yosi would take 10 dry dates to exempt 90 moist dates.

According to Shmuel, who follows the original volume, this is a tenth. Rav

follows the current volume. This is less than a tenth!

Answer (Rav Dimi): Dry dates are different (than meat). One can return them to their original state through cooking.

Yoma 73b (Mishnah): If on Yom Kipur one eats the volume of a big date and like its pit, he is liable.

78b - Question (Rav Papa): Is this with or without the pit?

Rav Ashi did not ask this, for it says 'big' - whatever way is bigger.

Nidah 54b (Mishnah): The following are Metamei only if they are moist -- Zov (emissions of uncooked semen from the Ever), Ni'a (thick mucus or spit) and (thin) spit (of a Zav, Nidah or Metzora), a Sheretz, a Nevelah, and semen;

If they are dry, but can become moist again if they are soaked (for 24 hours of soaking in lukewarm water), they are Metamei.

Uktzin 2:8 (Mishnah): If onion leaves and central shafts have Rir, we estimate them like they are. If there is a hollow, we compress it. We estimate spongy bread like it is. If there is a hollow, we compress.

Rishonim

Rambam (Hilchos Shevisas Asor 2:1): If one eats food the volume of a big date, which is slightly less than k'Beitzah, he is liable.

Question: The Mishnah says 'and its pit'. Why did the Rambam omit this?

Answer (R. Mano'ach): It is understood that the Shi'ur includes the pit, just like a k'Zayis, regarding which the pit is not mentioned. The Yerushalmi concludes that the Mishnah mentioned the pit to exclude the air pocket inside. The Rambam teaches that the Shi'ur is slightly less than k'Beitzah, so he did not need to discuss the pit and the pocket.

Rosh (Yoma 8:11): If one eats the amount of a large date and its pit he is liable.

Question: A dough was kneaded with eggs without water, and initially it did not have a Shi'ur to obligate taking Chalah, and it inflated and now it is twice as big as a normal dough obligated in Chalah. It should be liable, like we find regarding Shichchah (Peros that one forgot in the field. He must leave them for the poor). If a Nochri harvested his field, then converted, R. Yehudah obligates in Shichchah, for it depends on the time of Imur (making piles of detached Peros). Even though Shichchah applies also when the Peros are attached, and then he was exempt, since now it is obligated, he is obligated. Chachamim exempt only because they expound a verse. Regarding Chalah, all should obligate based on now!

Teshuvas ha'Rosh (2:14): Shichchah applies to attached Peros and to piles, one after the other. Therefore, it is reasonable to obligate piles even if they were exempt when they were attached. The Chiyuv Chalah comes only once, when putting the water on the flour. Since it was exempt at that time, even if it inflated later, it is still exempt. In Menachos, Rav concludes that if initially there was a Shi'ur, but now there is not, we follow the current size. If initially there was not a Shi'ur, but now there is, mid'Rabanan we follow the current size. Chachamim decreed Tum'ah or an Isur because now there is a Shi'ur. If we would be Metaher, an onlooker might think that initially there was a Shi'ur. This does not apply to Chalah. One who sees a big loaf assumes that Chalah was taken.

Suggestion: If a Se'ah of Terumah (grain) was mixed with less than 100 Sa'im of Chulin, and after grinding it increased, it is forbidden, for the Terumah increased like the Chulin. If we know that that Chulin was better (and increases more, and now it is 100 times the Terumah), it is permitted (Terumos 5:9). This is like the case of Chalah, and we are lenient. All the more so we should be stringent about Chalah!

Rebuttal (Rosh): There, Terumah and Chulin flour are mixed. If b'Shogeg Heter was added to a mixture and now there is a Shi'ur Bitul, it is permitted. Grinding b'Mezid is like adding b'Shogeg. A Kohen would grind such a mixture to eat it, so even if a Yisrael grinds, it looks like he intends to eat, and not for Bitul! We learn about Chalah from the Midbar. A dough is obligated only if it initially had a Shi'ur like an Omer (43.2 eggs) of manna. In truth, any dough kneaded with eggs is exempt.

Rashi (79a DH b'Gar'inisa): The Gemara asks whether the Shi'ur is like a date and its pit, or like it, (Bach - or) like its pit.

Tosfos (Yoma 79a DH Koseves): Rashi is difficult. What was the question? The Mishnah says 'and like its pit'! If the question was, perhaps it means 'or like its pit', if so, surely the date is without its pit. If so, what was the question? Surely the Shi'ur is both together. If it is one or the other, the Tana should just teach the smaller! Surely, they cannot be exactly the same. Rather, he asked whether the Shi'ur is a date like it is (with a pit) and another pit without a date, in all a date and two pits. Or, perhaps 'date' connotes without the pit, and 'and its pit' refers to the pit inside. The Aruch cites R. Nisim Ga'on, whose text in the Yerushalmi said 'one must compress the gap.' If not, it should say 'like it and its pit and its hollow.' A big date does not cling to the pit; there is a gap. Therefore, the Mishnah needed to say 'like a date and its pit' to be stringent not to measure like it is. Rather, one is liable for eating like it and its pit, without the gap. Here the Gemara asks whether the Shi'ur is a compressed date without the pit, or a compressed date as it is, with the pit.

Tosfos (54a DH d'Me'ikara): Our Gemara concludes that (even) according to Rav, we follow the current volume only mid'Rabanan. In Shabbos (91a), Rava asked about one who took half a Grogeres (to Reshus ha'Rabim) with intent to plant it, and it inflated (to a Grogeres), and he reconsidered to eat it. What was his question? Even if it swelled before he took it out, and he took it out from the beginning with one intent, he is exempt, for mid'Oraisa it depends on the initial volume!

Poskim

Rema (OC 486:1): One must compress the pockets of air in the vegetables (Maror), and gauge a k'Zayis of the vegetables themselves, and not the air in between.

Gra (DH uv'Yerakos): Tosfos brings from the Yerushalmi that one must compress the gap, like it says in Uktzin. However, in Menachos we conclude that the stringency of calf meat that inflated is mid'Rabanan. The Rambam rules like this. Rabah tried to answer for Shmuel, but in any case Shmuel is refuted, so we need not say that it is only mid'Rabanan, and that Ein Dichuy in Isurim. The Gemara in Shabbos (91a) never settled whether Yesh Dichuy. This also answers the question of Tosfos in Menachos. In several places, it seems that the Halachah is Yesh Dichuy. However, R. Shimshon and the Bartenura (Taharos 3:4) say that Ein Dichuy. They explain our Sugya simply (that even in the conclusion, Ein Dichuy). Also the Rambam and Rashba in Shabbos toiled to answer Tosfos' question. They did not say that our Sugya is unlike the Halachah. In practice, I cannot be lenient against them.

Mishnah Berurah (3): The same applies if there is a hollow in Matzah. If there is no hollow, even if it is soft and spongy, one need not compress it.

Sha'ar ha'Tziyon (7): Clearly, also for Birkas ha'Mazon we judge spongy bread like it is.

Kaf ha'Chayim (3): Here it seems that we gauge according to volume, and not according to weight. The custom is to gauge foods based on weight, in order to be Yotzei according to all opinions, and due to Safek Berachos. Surely, one need not weigh; it suffices to eat enough so that there is surely the proper Shi'ur. If for some reason one wants to eat only the Shi'ur, he should weigh the Matzah or Maror before Yom Tov.

Shulchan Aruch (210:1): One who eats less than a k'Zayis does not bless afterwards.

Mishnah Berurah (1): If bread was very spongy, so that one does not feel the air-pockets (I think this means that when he bites through pockets, his teeth do not feel the food), he does not bless for eating a k'Zayis of the bread, for he did not really eat a k'Zayis. If a k'Zayis shriveled, one does not bless after it unless it inflated again.

Shulchan Aruch (645:5): If most of the leaves of a Lulav (Rema - or its spine) dried, it is Pasul. Dry is when it ceases to be green, and whitens.

Rema: Some say that it is dry only if it can be crushed with a fingernail due to dryness. This is the custom in these lands, where Lulavim are not found.

Aruch ha'Shulchan (15): If some of the greenness returns after it is soaked in water, this is not called dry, and it is Kosher. We see that this happens. Regarding anything that changed, we follow how it is now, like it says in Uktzin and Menachos. If it returned to be green before Yom Tov, Dichuy does not apply at all. Even if it returned to be green on Yom Tov, we hold that Dichuy does not apply to Mitzvos.