1)

(a)Whatever is subject to Tum'as Ohel (as listed in the previous Perek), that is brought into a room in two halves R. Dosa ben Horkinas declares Tahor - because he maintains, the two halves do not combine to make up the Shi'ur.

(b)The Chachamim - declare it Tamei (because they hold that they do).

(c)The Mishnah continues by describing a case where someone touches two half-Shi'urim of Neveilah - to teach us that R. Dosa opinion extends to Tum'as Maga and Tum'as Masa, even with regard to Tum'as Neveilah.

(d)And likewise, in a case where the person carries two half-Shi'urim - R. Dosa ben Horkinas will hold Tahor.

2)

(a)The Chachamim on the other hand, hold in a case where ...

1. ... someone touches half a k'Zayis and is Ma'ahil on half a k'Zayis, is Ma'ahil on two half k'Zeisim k'Zeisim (see Tos. Yom-Tov), or if ...

2. ... he is Ma'ahil on half a k'Zayis and half a k'Zayis is Ma'ahil on him - that he is Tamei.

(b)To reconcile this ruling with the Seifa, which declares Tahor basically the same cases as the Reisha (see Tos. Yom-Tov DH 'O Ma'ahil al ka'Chatzi ... ' [even according to the Chachamim]) - we will establish the Reisha where there is not a Tefach space between the Tum'ah and the Ohel (Tum'ah Retzutzah), in which case it is considered as if one has actually touched the Tum'ah (so that both half Shi'urim are actually Tum'as Maga), whereas the Seifa speaks where there is, and Tum'as Maga and Tum'as Ohel do not combine (see Tos. Yom-Tov DH 'Ma'ahil al ki'Shenei ... ').

3)

(a)According to R. Meir - the Chachamim argue with R. Dosa in the Seifa too, and declare him Tamei - because in his opinion, Maga and Ohel fall under the same category (see Tos. Yom-Tov).

(b)R. Meir explains the Machlokes - by Maga and Masa or Ohel and Masa (or Heset [see Tos. Yom-Tov]), each of which are two different categories.

(c)The Halachah in the Machlokes between ...

1. ... R. Dosa and the Chachamim is - like the Chachamim.

2. ... the Tana Kama and R. Meir in the Chachamim is - like the Tana Kama.

(d)The principle that governs this ruling is that - two different types of Tum'ah cannot combine to create Tum'ah, whereas two halves of the same kind (Maga and Maga, Masa and Masa, and Ohel and Ohel [see Tos. Yom-Tov]) can.

4)

(a)The Tana Kama declares Tamei a M'lo Tarvad Rekev from a Meis that has scattered around the room (see Tos. Yom-Tov). R. Shimon disagrees - because other dust will inevitably have gotten mixed together with it, and in his opinion, M'lo Tarvad Rekev must comprise rot from the corpse exclusively (like the original Din of M'lo Tarvad Rekev).

(b)The Mishnah declare Tahor a room containing a Revi'is Dam from a Meis - once the blood has sunk into the ground (see Tos. Yom-Tov).

5)

(a)A Revi'is Dam that became absorbed in a Beged is Tamei - if washing the Beged extracts the blood, but Tahor, if it does not.

(b)One can know that washing has indeed extracted all the blood - by washing it in a bowl containing a specific amount of water, and comparing it with another bowl containing the same amount of water mixed with a Revi'is of blood.

(c)The principle that governs this ruling is that - whatever is absorbed and cannot subsequently be extracted, is Tahor.

6)

(a)The Mishnah now discusses a Revi'is Dam ha'Meis that spilt on to the floor of a room. Someone who is Ma'ahil over part of it (see Tos. Yom-Tov) is ...

1. ... Tahor - if it is flowing down a slope, because whatever is flowing down a slope is not considered joined.

2. ... Tamei, even though it is on a slope - if it has congealed.

(b)The Tana rules that in a case where the same Revi'is spilt on the threshold (see Tos. Yom-Tov) of a room (which is Ma'ahil on it), on to a slope that leads ...

1. ... inside - whatever is in the room is Tahor, and certainly if the slope leads ...

2. ... outside (see Tos. Yom-Tov).

(c)If the threshold is level ...

(d)... or the blood has congealed, then whatever is in the room is Tamei.

7)

(a)The Tana declares Tamei each and every independent part of a Meis - except for the teeth, the hair and the nails, which are Tahor.

(b)We learn ...

1. ... teeth from the word "ba'Etzem" - which teaches us that only what is created with the baby is ultimately subject to Tum'as Meis.

2. ... hair and nails from the same word - because it also teaches us that only parts of a body that will not grow back like before are subject to Tum'as Meis (see Tos. Yom-Tov DH 'Chutz min ha'Shinayim').

(c)Even these three parts of a Meis are Tamei however - as long as they are still attached to the Meis (see Tos. Yom-Tov DH 'u've'Sha'as Chiburo').

8)

(a)Based on what we just learned, if ...

1. ... the Meis is lying outside the room, but the hair is inside - whatever is in the room is Tamei, and the same will apply where ...

2. ... the bone of a Meis containing a k'Zayis Basar is basically lying outside the room, but a fraction is inside.

(b)The above two are Metamei be'Ohel whatever is inside the room - because the hair and the bone, are considered a Yad (handle) of the bone and of the Basar (see Tos. Yom-Tov), respectively.

(c)The Mishnah rules that if two bones each containing half a k'Zayis Basar (see Tos. Yom-Tov), are lying outside the room, but a fraction of each bone is lying inside - whatever is inside the room is Tamei.

(d)If the Basar was attached to the bones manually - then they are not Metamei, because, as we have learned a number of times, what man joins is not considered joined.

9)

(a)R. Akiva maintains that Dam Tevusah (which we learned in the previous Perek is Metamei be'Ohel) comprises an eighth of a Log from the Meis before he died plus an eighth after he died (see Tos. Yom-Tov DH 'Eizehu ... ' & 'Sheminis be'Chayav ... '). According to R. Yishmael - it is a Revi'is that is taken from a quarter of a Log from the Meis before he died plus a Revi'is after he died ...

(b)... but in R. Akiva's case, he holds that - a Revi'is is Tahor.

(c)R. Elazar b'R. Yehudah disgrees with both of the above opinions. When he says 'Zeh va'Zeh ka'Mayim', he means that - in both of the above cases, the blood is Tahor ...

(d)... and he defines Dam Tevusah as - blood that is flowing from a hanging man, that is forming a pool underneath him (see Tos. Yom-Tov).

10)

(a)According to R. Elazar b'R. Yehudah, blood that is dripping from a Meis to form a pool is Tahor - because each drop that drips from him becomes Bateil in the pool that has already collected.

(b)R. Yehudah maintains the reverse. He declares the blood that is ...

1. ... flowing from a hanging man, Tahor - due to the possibility that the last drop with which his Neshamah left him, remained on the tree from which he was hanging (see Tiferes Yisrael & Tos. Yom-Tov).

2. ... dripping from a Meis, Tamei - because R. Yehudah follows his opinion elsewhere that Miyn be'Miyno Eino Bateil (Something does not become Bateil in its own kind).

(c)The Halachah is - like R. Akiva (see also Mishnah Acharonah).

11)

(a)Keilim that are lying on the threshold of a number of doorways (with closed doors) leading from a room in which there is a k'Zayis min ha'Meis - all become Tamei.

(b)The principle that governs this ruling is - that any doorway, or potential doorway, though which one intends to transport a Meis is subject to Tum'ah (as if it was open).

(c)Its source is Gezeirah de'Rabbanan.

12)

(a)All the Keilim ...

1. ... barring those on one of the theshholds will remain Tahor - if one had the specific intention of carrying out the k'Zayis of Meis via that one.

2. ... lying on the thresholds will remain Tahor - if one had the express intention of carrying out the k'Zayis of Meis via a window of at least a square Tefach.

(b)If there is a complete Meis in the room - the window will have to be at least four by four Tefachim.

(c)For Keilim in the room on the other side of the window (or on the windowsill in the other room [Tos. Yom-Tov]) to become Tamei however - a window the size of a square Tefach will suffice.

13)

(a)The Mishnah rules that a piece of Meis that is larger than a k'Zayis - has the Din of a Meis (in which case the aforementioned window will need to be four by four Tefachim to render Tahor the Keilim on all the other thresholds.

(b)According to R. Yossi, if it is a Shedrah or a Gulgoles that is lying in the room (even though it contains less than a k'Zayis Basar) - it has the Din of a complete Meis.

(c)... and the Halachah - is like him (see Tos. Yom-Tov).

14)

(a)The Mishnah ascribes to a plank that measures a square Tefach, the status of - Meivi es ha'Tum'ah ve'Chotzetz bi'fenei ha'Tum'ah.

(b)A Tefach high means - that there is a Tefach between the Tum'ah and the plank (see Tos. Yom-Tov).

(c)The Tana adds the word Merubeh to teach us that - it must measure at least one Tefach by one Tefach (additional length does not make up for deficient width.

(d)After having said Meivi es ha'Tum'ah ve'Chotzetz bi'fenei ha'Tum'ah', the Tana continues with Keitzad - to describe Chotzetz bi'fenei ha'Tum'ah.

15)

(a)The Tana now discusses a sewage pipe that runs underneath a house into the street. Bib she'Hu Kamur means that - the pipe is covered (see Tos. Yom-Tov).

(b)If a piece of Meis is lying in the room above, the other two conditions that are required for whatever is in the pipe to remain Tahor, and for whatever is in the room to remain Tahor if it is lying in the pipe are that - the pipe itself and its opening to the street are both a square Tefach (as we explained).

(c)The pipe is not Tamei via the opening of the room into the pipe - because the piece of Meis is going to be removed from the room via the door and not via the pipe.

16)

(a)Assuming the pipe is a Pose'ach Tefach, but its opening into the street is not, then if the Tum'ah is in ...

1. ... the pipe - whatever is in the room is Tamei (see Tos. Yom-Tov).

2. ... the room - whatever is in the pipe remains Tahor ...

(b)... for the same reason as we just gave at the end of the previous answer.

(c)But if ...

1. ... neither the pipe nor the exit measures a square Tefach - then both the room and the pipe are Tamei, and the same will apply if ...

2. ... the pipe does not measure a square Tefach, but the exit does.

(d)Based on the Pasuk in Chukas "Kol asher ba'Ohel Yitma", the reasoning behind the latter Halachah is that - the floor of the room is like the room itself, and if the hole is less than a Tefach deep, then it is considered part of the floor, which in turn, is Tamei all the way down to the center of the earth (see Tos. Yom-Tov).

17)

(a)The Mishnah rules that a hole that is caused by ...

1. ... water having eaten into a wall (see Tos. Yom-Tov), one that has been made by Sheratzim or one that has been caused by corrosion (due to the salt content of the earth) - are all considered an Ohel to transmit Tum'ah to the other side (see Tos. Yom-Tov).

2. ... stones (Marbech shel Avanim [see Tos. Yom-Tov]) or beams that have been arranged in a orderly pile - and which form an Ohel, are likewise considered an Ohel and transmit Tum'ah from one side to the other.

(b)R. Yehudah disagrees with the Tana Kama. Based on a Gezeirah-Shavah "Ohel" "Ohel" (from Mishkan [see Tos. Yom-Tov]), he rules that an Ohel that is not man-made - is not considered an Ohel.

(c)He concedes however, that an Ohel in Shekifim or in Sela'im - one of which is natural, the other, formed by the rain, has the Din of Ohel.

(d)The basis for this ruling is that - the current holes are more than a square Tefach, and his earlier ruling is confined to one that is exactly a square Tefach.

(e)The Halachah is - like the Tana Kama.