Answer (Rav Nachman bar Yitzchak - Mishnah): (Mei Chatas, i.e. water mixed with ashes of the Parah Adumah, is an Av ha'Tum'ah.) If a cow drank Mei Chatas [and it was still in its stomach when it was slaughtered], the meat is Tamei;

R. Yehudah says, the Mei Chatas is Batel in its stomach [because it cannot be used to Metaher].

If he retracted only regarding Kelim, why is the Mei Chatas Batel - granted, it lost severe Tum'ah (it is no longer an Av), but it should retain light Tum'ah [of liquids, from having 'touched' itself when it was an Av, and Metamei the meat]!

Rejection: Perhaps it is Batel only regarding severe Tum'ah, but it retains light Tum'ah!

Question: This would imply that the first Tana says that it retains severe Tum'ah - if so, why is he Metamei only the meat [the water can Metamei even people and Kelim]!

Answer #1: The entire Mishnah is R. Yehudah - it is abbreviated, it means as follows:

If a cow drank Mei Chatas, the meat is Tamei;

The Mei Chatas has only light Tum'ah, but not severe Tum'ah, for R. Yehudah says that it is Batel in its stomach.

Answer #2 (Rav Ashi): The Mei Chatas is totally Batel, for it is a spoiled liquid (no one would drink it after the cow did).

(Beraisa - R. Yosi and R. Shimon): Kelim [that doubtfully became Temei'im through liquids] are Tehorim; food [that doubtfully became Tamei through liquids] is Tamei.

(Rabah bar bar Chanah): R. Yosi holds like his Rebbi, R. Akiva, who expounds "Yitma" like 'Yetamei':

(Mishnah): On that day [that R. Elazar ben Azaryah was appointed Nasi], R. Akiva expounded "V'Chol Keli Cheres Asher Yipol Mehem [El Tocho (if a Sheretz falls into an earthenware oven) Kol Asher b'Socho] Yitma" - It does not say 'Tamei', rather "Yitma" [which can be read 'Yetamei'], to show that a loaf [that was inside,] which is a Sheni makes a Shelishi [even] regarding Chulin.

Question: How does R. Yosi expound here?

Answer: It says "V'Chol Mashkeh Asher Yishaseh b'Chol Keli Yitma" - the liquid Yetamei (is Metamei) food.

Suggestion: Perhaps it is Metamei liquids!

Rejection #1: This is not so.

Question: What does this mean?

Answer (Rav Papa): We do not find Tum'ah (food or drink) that is Metamei like itself (Rashi - like we shall expound on Amud B; Tosfos - like we expounded above (14A)).

Rejection #2 (Ravina): The verse shows that it is not Metamei liquids - if it was, the Torah would not have written "Yitma" twice, regarding food and regarding liquids [since both Metamei liquids] - it would have written them together - 'Mi'Kol ha'Ochel...v'Chol Mashkeh...Yitma';

Rather, it says "Yitma" twice because [they are different,] food is Metamei liquids and liquids are Metamei food.

Question: Perhaps liquids are Metamei Kelim!

Answer: A Kal va'Chomer disproves this - Kelim are Metamei liquids, but they are not Metamei Kelim (Daf 20 A-B) - all the more so, a liquid that received its Tum'ah from a Keli cannot Metamei Kelim!

Question: Perhaps a liquid Nitma through a Keli cannot Metamei Kelim, but a liquid Nitma through a Sheretz can!

Answer: The Torah does not [explicitly] write about a liquid Nitma through a Sheretz - we only learn it from a Kal va'Chomer:

A liquid Nitma through a Keli (a Rishon) is Metamei liquids - all the more so, a liquid Nitma through a Sheretz (an Av) is Metamei liquids!

Dayo (it suffices) to learn from a Kal va'Chomer all stringencies found in the source [but we cannot learn more].

Question: What do we learn from "Yitma" regarding food?

Answer: "Mi'Kol ha'Ochel Asher Ye'achel...Yitma" - a food Yetamei (is Metamei) liquids.

Suggestion: Perhaps it is Metamei Kelim!

Rejection: A Kal va'Chomer disproves this - liquids are Metamei food, but they are not Metamei Kelim - all the more so, a food that received its Tum'ah from a liquid cannot Metamei Kelim!

Therefore, Yitma teaches that food can Metamei liquids, which are prone to become Tamei (this will be explained).

Question: Why do we need to say that it is Metamei liquids because they are prone to become Tamei - there is nothing else it could teach about (it cannot Metamei food like itself)!

Answer: One might have thought that since food is stringent, i.e. it can Metamei liquids (Tosfos R. Peretz - which were not Huchshar), it can also Metamei Kelim - we rebut this, this is not because food have a potent Tum'ah, rather, because liquids are prone to become Tamei.

Question: Why are liquids considered prone to become Tamei?

Answer: They are Mekabel Tum'ah without Hechsher.

The Torah wrote "Yitma" [as opposed to Yetamei] to teach that it does not Metamei [some things, e.g. another liquid] like itself.

Question: We learn this from another source!

"V'Chi Yutan Mayim Al Zera v'Nofal mi'Nivlasam Alav Tamei Hu" - it is Tamei, but it is not Metamei like itself.

Answer: That teaches about [food, and the same applies to] liquids that became Tamei through a Sheretz, and "Yitma" teaches about liquids that became Tamei through a Keli - both of them are needed:

Had it taught only about liquids that became Tamei through a Keli, one might have thought that liquids that became Tamei through a Sheretz, which are more severe, make Tum'ah like themselves. (And had it only taught about liquids that became Tamei through a Sheretz, we would not know that liquids that became Tamei through a Keli can Metamei at all:)

Note: Tzlach did not understand this. Due to Dayo, liquids that became Tamei through a Sheretz cannot be more severe than liquids that became Tamei through a Kli! Beis She'arim (YD 415) answers that Tosfos (DH Dayo) proved that the latter are a Sheni l'Tum'ah, but the former are a Rishon l'Tum'ah, so they could have this additional stringency.

Question: The Torah should have taught about liquids that became Tamei through a Sheretz - we would know that all the more so, liquids that became Tamei through a Keli do not Metamei like themselves!

Answer: A verse teaches this even though we could have learned from a Kal va'Chomer.

Question (Ravina): But Rava taught that R. Yosi does not hold like R. Akiva [who says that Chulin can become a Shelishi], and R. Akiva does not hold like [the following Kal va'Chomer of] R. Yosi! (If R. Yosi expounds Yitma like 'Yetamei', he must agree that Chulin can become a Shelishi!)

Answer (Rav Ashi): R. Yosi said that R. Akiva [who holds that Tum'ah of liquid is mid'Oraisa] should expound "Yitma" like 'Yetamei', but R. Yosi himself argues.

Question (Rav Ashi): I understand that R. Yosi does not hold like R. Akiva:

(Beraisa - R. Yosi): We learn that Kodesh can become a Revi'i from a Kal va'Chomer.

A Mechusar Kipurim (a Zav, Zavah, Yoledes or Metzora who has completed all steps of the Taharah process except for bringing Korbanos) may eat Terumah, but he is Posel Kodesh - a Shelishi is forbidden regarding Terumah (if Terumah is a Shelishi, it is forbidden), all the more so it is Posel Kodesh (makes a Revi'i)!

The following verse teaches that Kodesh can become a Shelishi; the above Kal va'Chomer teaches that it can become a Revi'i;

"Veha'Basar Asher Yiga b'Chol Tamei Lo Ye'achel" - even if it touched a Sheni [Kodshim becomes a Shelishi].

If R. Yosi held like R. Akiva, he would Posel a Revi'i of Terumah and a Chamishi of Kodesh! (A Tevul Yom may eat Chulin, but he is Posel Terumah - a Shelishi is Pasul regarding Chulin, all the more so it is Posel Terumah! We would then say that a Mechusar Kipurim may eat Terumah, but he is Posel Kodesh - a Revi'i is forbidden regarding Terumah, all the more so it is Posel Kodesh (makes a Chamishi!)