(Mishnah): The Chachamim only obligated bakers to separate Terumas Maaser and Challah.

Shopkeepers may not sell Demai (until they tithe it). And whoever sells in large quantities, such as wholesalers and grain sellers, may sell produce as Demai (without tithing).

(Gemara) Question: The Mishnah (in Perek 5) teaches - "if one buys from a baker, how does he tithe?" meaning that the buyer tithes, and here (in our Mishnah), you said that the baker must tithe?

Answer (R. Yona): The resolution is a dispute between R. Elazar and R. Yochanan - one answered that in our Mishnah, the baker is producing it in a state of Taharah (so the Chachamim obligated him to separate Terumas Maaser and Challah before it would become Tamei by the time it would reach buyer's hands); the later Mishnah refers to a baker producing it in a state of Tumah. The other opinion answered that in our Mishnah the baker is selling small quantities and in the later Mishnah, he is selling in large quantities (and as our Mishnah taught, whoever sells in large quantities may sell Demai). However, it is unknown as to which answer was said by whom.

But since R. Yochanan explained that our Mishnah required the bakers to tithe so that it should be done in Taharah, this shows that R. Elazar's answer was about the different quantities.

Question: According to R. Yochanan, why doesn't he tithe everything (even Maaser Sheni)?

Answer: Strictly speaking, he should not separate anything; however, one may not give Taharos to an Am HaAretz.

Question: (Against Reish Lakish) if he's selling in small quantities, why doesn't he tithe everything? (The Gemara doesn't answer this question.)

The Mishnah taught - Shopkeepers may not sell Demai (until they tithe it).

(Chevraya citing R. Elazar): This Tanna is R. Meir, who said that they only permitted a wholesaler to sell Demai.

Question (R. Yosi): But the Mishnah itself disproves this, as it taught, "And whoever sells in large quantities, such as wholesalers and grain sellers" - this shows that they not only permitted the wholesalers; they even permitted others who sell in large quantities...? (This shows that the Mishnah is not like R. Meir.)

Answer (R. Yosi): Rather, R. Ila was referring to a Baraisa when he said that it is R. Meir - 'When were they lenient to allow a baker to only separate Terumas Maaser? When he is selling in his store or at its entrance i.e. in public (where the government officials see him and make him reduce the price; then he is exempt from Maaser Sheni); but if he was selling it in a Palter (gentile bakery) or in his store close to the Palter, (he will not be noticed by the government officials who make him reduce the price, so) he must also separate Maaser Sheni'. The Chevraya said from R. Elazar that this is the opinion of R. Meir, and that is the R. Meir that we discussed.

The Mishnah that follows our Mishnah says - R. Meir says - if something usually measured out in large quantities was measured in a small quantity, the small quantity is treated as if it is large (and the seller is not required to separate Maaser Sheni).

R. Chiya (Baraisa): If something usually measured out in large quantities was measured in a small quantity, it's treated like a small quantity (and the seller is required to separate Maaser Sheni). Similarly, if he selling (without the officials troubling him) in small quantities, even though in his store he sells in large quantities, it is given the law of small quantities (and is obligated in Demai).