(The Mishnah prohibits buying water and salt with Ma'aser Sheni money, but therefore allows fish, grasshoppers and mushrooms.) This follows the opinion of R. Akiva and not R. Yishmael...

R. Yishmael expounded - the pasuk states (Devarim 14:26), "And you shall turn that money into whatever your soul desires'' - that is a generalization; "cattle, sheep, wine or beer'' - they are specifications; "or whatever your soul desires'' - is another generalization. When there is a generalization, then a specification, then another generalization - you only include that which is like the specification. Just as the specifications are things that grow from the ground or things that are derived from that; so too one must purchase something that grows from the ground or something derived from that.

R. Akiva explained that just as the specification is a product, it comes from a product (e.g. wine comes from grape pulp) and it gives flavor to other products (e.g. wine is used to flavor a dish); so too one must purchase something that is a product, it comes from a product and it gives flavor to other products.

What's the practical difference between (R. Yishmael and R. Akiva)? Fish, grasshoppers and mushrooms may be bought with Ma'aser Sheni money according to R. Akiva.

(R. Chagai): The Mishnah taught (about one who inadvertently used Ma'aser Sheni money to buy produce outside Yerushalayim. This) teaches that one cannot transfer the Kedushah of Ma'aser Sheni money onto produce that is outside Yerushalayim.

R. Chagai said it in front of R. Avina and he praised it. He said it in front of R. Yirmiyah and he criticized it, asking from the later Mishnah (in Perek 3), 'If a person had Ma'aser Sheni money in Yerushalayim and Chulin produce outside Yerushalayim (he may exchange it by saying...)'. (This shows that one may transfer money onto produce that is outside Yerushalayim...?)

Rebuttal: That's different, because one of the two (the money or the produce) are inside Yerushalayim.

When R. Chagai left, he discovered a Baraisa that taught that if they are both inside or both outside Yerushalayim (one may transfer...). He said, "If R. Yirmiyah would have heard that Baraisa, he would certainly have had his question.''

As a result of this Baraisa, R. Chagai wished to retract his ruling.

(R. Zeira to R. Chagai): Don't retract, as R. Elazar explained that the Mishnah (in Perek 3) follows all opinions (even though R. Meir and the Chachamim disagreed in a Mishnah in Maseches Demai (1:2) over exchanging Demai).

However, according to R. Imi who said that the Mishnah (in Perek 3) is the opinion of R. Meir, both Demai and certain Tevel are the same.