1) CRANIAL DRILLS
QUESTION: The Gemara earlier (37b) quotes the Mishnah in Ohalos (2:3) in which Beis Shamai and Beis Hillel argue about the degree of damage or deficiency a body part must have in order that it not be Metamei b'Ohel. Beis Shamai says that a skull with a hole is not Metamei b'Ohel when the hole is the size of the hole made by a surgeon's drill. Beis Hillel says that a skull is not Metamei b'Ohel when it has a hole that would cause a living person to die. Rav Tachlifa bar Avodimi in the name of Shmuel explains that a hole the size of a Sela coin would cause a person to die.
Rav Chisda there questions Rav Tachlifa's explanation from the Mishnah in Kelim (17:12) that says that a hole the size of a Sela and a hole the size of a drill-hole are the same size, and yet it is clear that Beis Shamai and Beis Hillel are arguing with each other. According to Rav Tachlifa, what is their argument?
Rav Nachman answers that a large drill makes a hole the size of a Sela Nironis (a Sela of Nero), which is larger than the size of an ordinary Sela. Thus, Beis Shamai requires the hole to be larger in order for the skull not to be Metamei.
RASHI (DH b'Eizeh Makde'ach) explains that the surgeon uses his drill in order "to pierce the head to heal a wound." If the drill is used to pierce skulls for curative purposes, then it is obvious that a person can live with a hole in his cranium the size of the surgeon's drill-hole! Why, then, does Beis Hillel say that a hole smaller than the size of a drill-hole causes a person to die?
Moreover, the Gemara in Eruvin (7a) teaches that the Shi'urim of Beis Hillel and Beis Shamai apply not only to the laws of Tum'as Ohel, but also to the laws of Tereifah. Beis Shamai, who says that a large hole in the skull renders the skull unable to be Metamei b'Ohel, also maintains that a large hole must be missing in order for an animal to become a Tereifah. The Gemara in Eruvin implies that the Shi'ur that Beis Shamai describes as the size of a surgeon's drill is the amount of missing cranial bone that will render an animal (or a person) a Tereifah. If a hole of this size causes an animal to become a Tereifah, then how can the surgeon's drill be used to heal a person by piercing his skull? A hole of that size should make the person a Tereifah! (M. KORNFELD)
(a) Perhaps when Beis Hillel mentions the Shi'ur of a hole that will cause a living person to die, he means that it will cause a person to die if it is not filled or covered. Immediately after the procedure, the surgeon covers the hole he made, thereby preventing the person from dying. (Y. Tavin)
However, this answer explains only why the surgeon's hole can be larger than the hole that causes a person to die. It does not answer how the hole can cure a person while at the same time it renders a person a Tereifah. The Gemara in Chulin (57b) teaches that when a hole renders an animal a Tereifah, medical intervention does not prevent the animal from dying. Therefore, covering the hole that makes a person a Tereifah should not prevent him from dying.
(b) RAV MOSHE SHAPIRO shlit'a suggests that perhaps the surgeon's drill is not used in the same place on the skull where a hole will render a person a Tereifah. A hole will render him a Tereifah only in certain parts of the skull. When Rashi mentions that a surgeon's drill is used to cure a person, he does not mean that it is used on the same part of the skull which Beis Shamai is discussing in the Mishnah.
(c) Rav Moshe Shapiro suggests further that perhaps a hole that normally renders an animal or person a Tereifah will not render him a Tereifah when it is made under controlled conditions during a surgical procedure.
When Beis Hillel mentions a hole large enough to cause a living person to die, he is referring to a hole that is made without medical supervision. A surgeon, however, can remove even large amounts of the skull without killing the person, because he does it under surgical conditions.
2) A SUNKEN "DAK" AND A FLOATING "DAK"
OPINIONS: The Gemara quotes a Beraisa that teaches that a Dak that appears sunken into the eye is a Mum, while a Dak that appears to be floating on the surface of the eye is not a Mum. The Gemara questions this from a second Beraisa that says that a sunken Dak is not a Mum, while a Dak on the surface is a Mum. The Gemara answers that the first Beraisa is discussing a black Dak, while the second Beraisa is discussing a white Dak.
What is a sunken Dak?
(a) RASHI (DH Dak) explains that it is a thin film that develops due to an eye-disease, which causes a recession of the eye itself.
(b) The SHITAH MEKUBETZES (quoted in SEFER MIZBE'ACH KAPARAH) asks that if the eye itself is recessed, then the text of the Beraisa should read "Meshuka'as," because the word "eye" in Hebrew is treated as a feminine term and thus warrants a verb in the feminine form. The RI MI'PARIS therefore explains that a sunken Dak refers to a case of a thin film that is itself recessed into the eye.
(It is possible that this is also Rashi's intention. Rashi writes that "the Dak causes the 'eye' to become recessed" in order that one not mistakenly assume that the Dak is actually sunken underneath the surface of the eye. By explaining that the eye is recessed, Rashi teaches that the Dak is on the surface of the eye but that there is a depression in the eye filled by the Dak.) (M. KORNFELD)
3) A PERMANENT BLEMISH THAT MIGHT HEAL
QUESTION: Rabah bar bar Chanah related that Rebbi Yoshiya of Usha told him that a black Dak in the eye is considered a Mum when it is sunken in the eye, but it is not considered a Mum when it appears to be floating on the surface. Conversely, a white Dak is not a Mum when it is sunken in the eye, but it is a Mum when it appears to be floating on the surface (see previous Insight). The Gemara says that the mnemonic for remembering which type of Dak is a Mum and which is not a Mum is the word, "Barka." RASHI (DH v'Simaneich) explains that a "Barka" is a type of a white spot that appears to be floating on the surface of the eye, and it is known to be a Mum. Since one easily remembers that a Barka is a Mum, he will remember that the white Dak is a Mum when it is floating, but not when it is sunken (and, by inference, the black Dak is a Mum only when sunken, but not when floating on the surface).
TOSFOS (DH v'Simaneich) points out that the Gemara here clearly implies that a Barka is considered a Mum. However, the Gemara in Gitin (69a) states that there are cures for a Barka. Similarly, the Gemara in Shabbos (78a) states that one may apply blue dye to the eye in order to heal a Barka! Why, then, is a Barka considered a Mum, if it is easily healed? Tosfos (in his second answer) explains that a Mum that cannot heal naturally is considered a Mum even though it can be healed through medical intervention. Therefore, a Barka -- which does not heal naturally but only through medical intervention -- is considered a Mum.
Tosfos' assertion that a blemish is considered a Mum as long as it does not heal naturally seems problematic in light of the Gemara in Chulin (46b). The Gemara there cites Rava who says that an animal is a Tereifah when part of its lung is dried out. The Gemara explains that if it is dry enough that it can be crushed by a fingernail, then the animal is a Tereifah. The Gemara suggests that Rava agrees with Rebbi Yosi ben Hameshulam who states in the Mishnah (Bechoros 37a) that dryness in the ear is considered a Mum on a Bechor only if it is so dry that it can be crushed by the fingernails.
According to Tosfos, what is the Gemara's comparison between a Mum that renders an animal a Tereifah and a Mum that invalidates a Bechor? There is an essential difference between a Tereifah and a blemished Bechor, as the Gemara in Chulin (54a) teaches: when a wounded animal will live if medication is applied to its wound, it is not considered a Tereifah. According to Tosfos, a wound in a Bechor that will heal only as a result of applying medication is still considered a Mum! How, then, can the Gemara in Chulin say that Rava would agree with Rebbi Yosi ben Hameshulam and invalidate a Bechor only when its lung is so dry that it can be crushed by a fingernail? Perhaps Rava does not follow the view of Rebbi Yosi ben Hameshulam, and he maintains that even before the lung is so dry that it can be crushed by a fingernail, it is considered a Mum with regard to a Bechor, since the only way that it can heal is through medical intervention!
ANSWER: The ACHIEZER (2:25:1) answers that the Mum of dryness differs from a Mum caused by a hole in an exposed place (such as a hole in the Ris of the eye, mentioned in the Mishnah here (38a)). A hole in an exposed place is a Mum because of the present defect in the animal. In contrast, dryness is a Mum because it is similar to an illness. Once it has become so severe that no blood will come out when a hole is made in the organ (according to the Tana Kama (37a)), or it is so dry that a fingernail can crush it (according to Rebbi Yosi ben Hameshulam), the organ no longer is considered to have any vitality; it is considered as though the organ is entirely missing and the animal is a Tereifah. (This is similar to the RAMBAM's statement (in Hilchos Shechitah 8:7) that when there is a place in the lung which is so dry that it can be crushed by a fingernail, it is considered as if this place is missing entirely, and therefore the animal is a Tereifah.) Since dryness is an illness, it is similar to a Tereifah, and, therefore, if it can be healed so that it no longer renders the animal a Tereifah, then it can also be healed so that it is no longer considered a Mum in a Bechor.
Tosfos' statement -- that even a permanent blemish, a Mum Kavu'a, can be healed so that it is no longer considered a Mum -- applies only to a Mum that causes a present defect in the animal, such as a hole in an exposed place, but not to a Mum that is a Mum because of illness. (See Insights to Bechoros 33:3
, in the name of the Achiezer who also explains Rashi there (DH Ein) and Rashi in Zevachim (74b, DH Nekuvas) according to this approach, that an illness that is curable is not a Mum at all.) (D. BLOOM