1)

(a)The Gemara attempts to prove that Rebbi Akiva, who holds of a Shelishi l'Tum'ah by Chulin, does not hold like Rebbi Yosi - by the mere fact that there is no Tana who talks of a Revi'i by Terumah or a Chamishi by Kodesh.

(b)The Gemara queries this proof on the grounds that this is too weak a proof to be conclusive.

(c)'A vessel combines all that is in it by Kodesh, but not by Terumah' - means that if a vessel contains two items of Kodesh, and Tum'ah touches one of them, the other item becomes Tamei too, even if the two items are not touching each other (because the vessel - which does not receive Tum'ah from food, min ha'Torah - combines into one whatever is inside it). This Halachah is confined to Kodesh, and does not extend to Terumah.

(d)Rebbi Akiva says in another Mishnah that if a Tevul-Yom touched either the flour, the incense, the frankincense or the coal that were all lying in one vessel, he renders them all Tamei (even though they are not touching each other, and even though they are not food. So we see that a vessel which contains various items of Kodesh, combines them all for Tum'ah; and now that Rebbi Yochanan connects the two Mishnahs, we also see that Rebbi Akiva holds of a Revi'i ba'Kodesh, but not of a Chamishi.

2)

(a)If Rebbi Akiva were to hold of the Kal va'Chomer of Rebbi Yosi, he would learn a Revi'i by Terumah from a Kal va'Chomer from a Tevul Yom (who is permitted to eat Chulin, but Pasul from eating Terumah), a Shelishi, who is Pasul by Chulin, should certainly make a Revi'i by Terumah; and he would then go on to learn a Chamishi by Kodesh, exactly as Rebbi Yosi does (see end of Daf 18b). The reason that he rejects this set of Derashos is because, in his opinion, we cannot learn the Din of a Shelishi from a Tevul-Yom, since a Tevul-Yom (in spite of its leniency) is an Av ha'Tum'ah, whereas a Shelishi is a Toldah.

(b)According to Rebbi Akiva, we find a Revi'i b'Tum'ah d'Oraisa by Kodesh, like this - a Sheretz touches a vessel, the vessel touches food, the food liquid and the liquid, food.

(c)According to Rebbi Yosi, who does not hold of "Yitma" 'Yetamei', liquid cannot transmit Tum'ah (even) to food, min ha'Torah. Consequently, even though he learns a Revi'i ba'Kodesh from a Kal va'Chomer, that can only be a Kal va'Chomer mid'Rabanan. And the proof for this lies in the fact that it is listed among the decrees mid'Rabanan in the last chapter of Chagigah (See Tosfos DH 'Lo').

3)

(a)The case of a Shelishi l'Tum'ah d'Oraisa by Kodesh, according to Rebbi Yosi - is when a Sheretz touches food, the food touches other food, which touches liquid (which, according to Rebbi Yosi, can receive Tum'ah, but not transmit it). Clearly, Rebbi Yosi is of the opinion that something which is Tamei, can transmit Tum'ah to its own kind - by Kodesh.

(b)Rebbi Yosi and his colleagues learn that food renders liquid Tamei - from the Pasuk "Tamei Hu" 'Hu Tamei, v'Ein Oseh Keyotze Bo' (by Chulin), from which we can infer that it (food) can render other things, of a different kind i.e. liquid, Tamei.

(c)When Rebbi Yirmeyahu (above, end of 15b) explained that Rebbi Yosi was following his own reasoning i.e. that liquid transmits Tum'ah mid'Oraisa - he was referring, not to his personal opinion, but to his interpretation of that of his Rebbe, Rebbi Akiva.

4)

(a)Frankincense and coal of Kodshim are subject to Tum'ah, in spite of the fact that they are not food - because of 'Chibas ha'Kodesh' (presumably because they are, kev'Yachol, the food of Hash-m).

(b)If the flour, incense, frankincense and coal lying in a vessel, which were touched by a Tevul-Yom, were all Tamei, because they received Tum'ah from each other (and not because of Tziruf Kli), that would make them a Shelishi, a Revi'i, a Chamishi and a Shishi, depending upon the order that they touched each other. And this is impossible, because the highest level of Tum'ah by Kodesh is a Revi'i, as we have just learnt.

(c)According to Rebbi Yochanan, the Gemara says, Tziruf Kli is only mid'Rabanan - because a. the Mishnah that he quoted is that in Chagigah, which lists only decrees d'Rabanan (as we stated earlier), and b. because coal and frankincense are not subject to Tum'ah min ha'Torah (since they are not food, and Chibas ha'Kodesh is only mid'Rabanan).

(d)Rav Chanin learns from the Pasuk "Kaf Achas Asarah Zahav Melei'ah Ketores" - that a vessel which contains various items of Kodesh, combines them all, and renders them all Tamei. According to him, Tziruf Kli is d'Oraisa.

5)

(a)If a needle is found in the flesh of a Kodshim animal, the flesh is Tamei - whereas if it is found in its dung, it is Tahor.

(b)Rebbi Akiva derives from the fact that this Mishnah in Iduyos renders the hands Tahor in both cases - that when Chazal decreed Tum'ah on Stam hands, that did not pertain to the Beis ha'Mikdash.

(c)Rebbi Akiva used the expression 'Zochim' - because due to his deduction, we are spared from many instances when we would have to declare Kodshim Tamei, rendering them Pasul. So Chazal's declining to decree Tum'ah here is a merit and a good thing.

6)

(a)The suggestion that Tum'as Kelim mid'Rabanan had not yet been decreed when this Mishnah was learnt, is wrong - on account of the Mishnah in Zavin, which clearly states that the decrees of Sefer, the hands ... and vessels were all decreed on the same day.

(b)The reason that Rebbi Akiva did not include Tum'as Kelim in his statement - is because the knife in our case would not have become Tamei even if it had been Chulin. Why not? Because how should it have become Tamei, if not through touching the flesh or through touching the needle; but neither food nor vessels can render vessels Tamei.

(c)According to those who say that Chazal did not decree on vessels that are found in Yerushalayim - why did they consider the needle that was found in the flesh, Tamei?

(d)The second answer to the Kashya is - that the cow was brought into Yerushalayim muzzled, in which case, the needle must have entered the cow's stomach outside Yerushalayim, where Safek vessels that are found are Tamei.

7)

(a)The Amora needs to inform us that Chazal did not decree Tum'ah on spittle that is found in Yerushalayim - even if a Zav was seen walking around in the same street where the spittle was found.

(b)We cannot infer from the Mishnah in Chagigah, which renders vessels found in Yerushalayim on the way down to the Mikveh, Tamei, that vessels found elsewhere are Tahor - because of the Seifa, which states 'Derech Aliyah, Tehorin', from which we can infer exactly the opposite: that anywhere else in Yerushalayim, they are Tamei. We need the Gemara therefore, to teach us that the Reisha is specific (and our inference is correct), but the Seifa is not.

(c)The reason that the Tana needs to add that vessels found on the way up from the Mikveh are Tahor - is to infer from there that vessels found in the small alleyways next to the paths leading down to the Mikveh, are Tamei, since we are not sure whether they were dropped there before they went down or after they came up; we do know however, that they were Tamei at one stage, and that is why they have a Chezkas Tum'ah.

8)

(a)The Gemara initially thought that since, according to Rav, the needle that rendered the flesh of the Kodshim animal, Tamei, was Tamei Mes, it should also be Metamei the person and the vessels - because of the principle 'Cherev, Harei Hu k'Chalal'.

(b)That is not the case, however, because, unlike the flesh, which definitely touched the needle, the person and the vessels are only a Safek, and, seeing as the Azarah is considered a Reshus ha'Rabim, we apply the principle 'Safek Tum'ah, bi'Reshus ha'Rabim, Tahor'.

(c)The Gemara queries the inference that, in an equivalent case in a Reshus ha'Yachid, the person and the vessels would be Tamei - due to the fact that a needle is something that cannot be asked whether it is Tamei or Tahor, and whatever cannot be asked etc., is Tahor even in the Reshus ha'Yachid (because it is not like Sotah, which is the source of the Din of Safek Tum'ah bi'Reshus ha'Yachid).

(d)Rebbi Yochanan says 'Safek Tum'ah ha'Ba'ah b'Yedei Adam, Nish'alin Aleha, Afilu bi'Cheli ha'Munach Al-gabei Karka, k'Davar she'Yesh Bo Da'as Lisha'el'. Here too, if the knife would have touched the needle, it would only have been through the person who was wielding it; consequently, it will have the Din of a 'Davar she'Yesh Bo Da'as Lisha'el'.

9)

(a)Rebbi Yochanan adds 'ha'Munach Al Gabei Karka' - to teach us that his statement applies even if the person was not actually dealing with the vessel which is the subject of the Safek (so he will not take it to the Beis-Din to ask - which is the meaning of 'Nish'alin Aleha'), but with the Sheretz which may have touched the vessel.