1) AN ANIMAL BORN WITHOUT A LIVER
OPINIONS: The Mishnah (42a) states that one of the Tereifos is an animal whose liver has been removed and nothing remains of it. The Gemara infers from this that if something does remain of the liver, even if it is less than a k'Zayis, then the animal is not a Tereifah. The Gemara asks that this seems to contradict the Mishnah later (54a) that states that if the liver was removed but a k'Zayis remains, the animal is Kosher. The Mishnah there implies that if less than a k'Zayis remains, then the animal is a Tereifah.
The Gemara answers that the Mishnayos indeed are arguing. One Mishnah follows the view of Rebbi Shimon bar Rebbi, while the other Mishnah follows the view of Rebbi Chiya (see two explanations in RASHI DH Matvil Lah).
The Mishnah here and the Mishnah later discuss only the status of an animal whose liver has been removed ("Nital"). Does the same Halachah apply to an animal that was born without a liver ("Chaser")?
(a) The RAMBAM (Hilchos Shechitah 8:24) rules that in any case in which the Gemara says that an animal is a Tereifah when it is missing a certain limb from birth ("Chaser"), the animal is also a Tereifah when that limb was removed later ("Nital"). However, in any case in which the Gemara says that an animal is a Tereifah when a limb was removed ("Nital"), the animal is not a Tereifah when the limb was missing from birth ("Chaser"). The Rambam rules this way because without this distinction there would be no difference between the cases of "Chaser" and "Nital," and yet the Gemara (43a, in the name of Ula) counts them as two separate types of Tereifos. Accordingly, an animal born without a liver is Kosher.
(b) The RASHBA rules that an animal born without a liver is considered a Tereifah, like an animal whose liver was removed.
The OR SAME'ACH (Hilchos Shechitah 8:24, DH v'Hineh) writes that the Gemara's question here seems to support the Rashba's ruling. If, as the Rambam rules, an animal is Kosher when it has a liver that is small (less than a k'Zayis) from birth, then the two Mishnayos do not contradict each other. The second Mishnah, that says that an animal is a Tereifah when it has less than a k'Zayis left of its liver, refers only to an animal born with a normal-sized liver and some of it was removed. In order for the animal not to be a Tereifah, at least a k'Zayis of its liver must remain. The first Mishnah, that says that an animal is a Tereifah when none of its liver remains, includes even an animal that has a small (less than a k'Zayis) liver from birth. When part of the liver is removed from such an animal, it does not become a Tereifah merely because the liver is now smaller than a k'Zayis, because even when it had its whole liver, its liver was smaller than a k'Zayis. Regarding such an animal, the Mishnah states that it will be a Tereifah only when its entire liver is removed. It must be that there is no difference between an animal born with a normal liver and an animal born with a small liver; in either case, if the liver (or remaining part of the liver) is less than a k'Zayis, the animal is a Tereifah.
(See Or Same'ach there who explains how the Rambam understands the Gemara here.) (D. BLOOM)
2) THE REASON WHY A "SIRCHAH" RENDERS THE ANIMAL A "TEREIFAH"
OPINIONS: Rava states that when there is a Sirchah (a growth of fibrous flesh that connects one part of the lung to another, or to part of the wall of the chest cavity) on the lung between two lobes, it is not possible to examine the lung for a perforation, and thus the animal is considered a Tereifah. However, this applies only when the Sirchah is between two lobes that are not directly next to each other. A Sirchah between two adjacent lobes does not render the animal a Tereifah, because it is considered a natural part of the growth of the lung.
What exactly is a Sirchah and why does it render an animal a Tereifah?
(DH Leis Lehu) explains that the Sirchah forms as a result of a hole in the lung. The lung absorbs various fluids, and the fluids thicken inside the lung. Some of the thickened fluid emerges through the hole in the lung and hardens, forming a membrane that blocks the hole. Even though the membrane seals the hole so that no air escapes through it, the law is that a membrane that develops in the lung does not prevent the animal from becoming a Tereifah because the membrane will disintegrate later (see Insights to 43:1
The HAGAHOS MORDECHAI (#739) asks -- according to Rashi's explanation that every Sirchah has a hole beneath it -- whether or not this law applies to a Sirchah on another organ. For example, what is the status of an animal that has a Sirchah protruding from the gall bladder, or from the thick part of the spleen? Does this also indicate that there is a hole in that organ? Perhaps Rashi maintains that only a Sirchah on the lung is always indicative of a whole, because the lungs absorb all sorts of fluids that harden and form Sirchos. Sirchos on the other organs do not develop from hardened fluids, and, therefore, they do not indicate that the animal is a Tereifah.
The TERUMAS HA'DESHEN (1:163) also discusses the status of Sirchos on other organs. He writes that perhaps the reason which Rashi gives for why a Sirchah on a lung is a sign of a Tereifah does not mean that a Sirchah formed from a hole is a phenomenon exclusive to the lung. Rather, Rashi gives this reason in order to explain why Sirchos are much more common on the lungs that on other organs. Since the lung absorbs so much fluid, it is common that Sirchos develop at holes in the lung. However, it could be that Sirchos develop for the same reason in other organs that are moist and absorb fluids (such as the intestines, spleen, heart, and liver). The Terumas ha'Deshen concludes that we should not be lenient with the prohibition of Tereifah, since we find that the authorities are very strict with regard to this prohibition.
(b) TOSFOS (DH Hainu) questions Rashi's explanation. If the presence of a Sirchah indicates that there is a hole in the lung, then why is the animal Kosher when the Sirchah is between two adjacent lobes? There still is a hole beneath the Sirchah that should render the animal a Tereifah!
Therefore, Tosfos gives a different explanation. Tosfos explains that a Sirchah is not the result of a hole in the lung, but it is the cause of a hole in the long. Since the animal's lungs absorb various fluids, it is common for a Sirchah to develop even when there is no hole in the lung. A Sirchah between two non-adjacent lobes renders the animal a Tereifah because the Sirchah eventually will tear off, pulling a part of the lung with it and leaving a hole in the lung. Even though the lung has not yet been pierced as long as the Sirchah is intact, since it eventually will become pierced it is considered to have a hole already. In contrast, a Sirchah between adjacent lobes does not pull at the lung, because this is the natural way that the animal develops, and a Sirchah in such a place will not cause a hole in the lung.
(Tosfos later suggests -- in defense of Rashi's explanation -- that a Sirchah between two adjacent lobes does not render the animal a Tereifah because even though there is a hole beneath the Sirchah, the membrane that forms in that place will be an effective seal, since the lobes lie naturally together and, therefore, the membrane becomes a strong seal.)
The PRI MEGADIM (introduction to YD 39, DH v'Yesh Lachkor) writes that according to Tosfos, who says that a Sirchah renders an animal a Tereifah because it eventually will make a hole in the lung, it follows that this Tereifah is a definite Tereifah, and not merely a Tereifah out of doubt. However, according to Rashi's explanation, it could be that this Tereifah is only a Tereifah out of doubt, and Rashi's statement, "There is no Sirchah without a hole," is not a statement of certainty, but rather it means that since there is a Sirchah, we must be stringent because of a doubt that there might be a hole beneath it.
Alternatively, perhaps the statement, "There is no Sirchah without a hole," is a statement of certainty, but nevertheless perhaps only the outer membrane was pierced and the animal is still Kosher (as the Gemara earlier concludes that a hole in the lung is considered a Tereifah only when both the outer and inner membranes were pierced).
The Pri Megadim concludes, however, that because the lungs absorb so much fluid, Sirchos are very common, and we must assume that the Sirchah definitely formed from a hole beneath it. (See also TESHUVOS REBBI AKIVA EIGER 2:21.) (D. BLOOM)
(See Insights to Chulin 49:1
regarding the practical Halachos of Sirchos found on lungs, and for the definition of what is commonly referred to as "Glatt Kosher" meat.)