(Mishnah): (The Maaser Sheni of) Demai is not obligated in (adding) a fifth, or in being removed (at the end of the third year of the Shemittah cycle); it may be eaten by a Onen (one who is before or on the day of burial of a close relative); it may be brought into Yerushalayim and then taken out (even though for regular Maaser Sheni, that is prohibited);

If there is a small amount, he may just waste it on the roads (rather than bring it to Yerushalayim if, for example, he was in a place of soldiers or bandits) and he may give it to an Am HaAretz and then eat the equivalent amount in Yerushalayim. (It is usually prohibited to give actual Maaser Sheni to an Am HaAretz.)

One may transfer the sanctity of Maaser Sheni of Demai from silver to silver, copper to copper, silver to copper and from copper back to fruit, as long as he then redeems the fruit onto money. This is the opinion of R. Meir.

(Chachamim): They must be taken and eaten in Yerushalayim.

(Gemara) (Question): Didn't Yochanan the Kohen Gadol cancel the law of declaring Maaseros?

Answer: He cancelled the requirement to make a declaration but not the requirement to remove it. This applied to definite Maaser Sheni but Maaser Sheni of Demai does not even require removal.

Baraisa: It may be eaten by an Onen but not in a state of Tumah.

Question: What's the difference?

Answer (Rav Nachman): Tumah is common; Aninus (being an Onen) is not; they only decreed on that which is common.

(R. Yosi): They didn't even make Maaser Sheni of Demai like Maaser Sheni of doubtful Tevel (doubtfully untithed produce) - doubtful Tevel is prohibited to an Onen, but Demai is permitted!

Question (Mishnah in Maseches Bava Metzia): (Discussing the five cases of 'fifths') (If one eats) Terumah, Terumas Maaser of Demai...(he must add a fifth to the value) - but in our Mishnah it taught that it is not obligated in (adding) a fifth...?

Answer (R. Zeira): It taught there the case of Terumas Maaser of Demai, but our Mishnah discussed Maaser Sheni of Demai (where according to the Torah, the fifth is not crucial).

Rebuttal (R. Imi): Our Mishnah also discussed Terumas Maaser of Demai. So what is the resolution? Over there was the opinion of R. Meir; here was Rabbanan (the dispute being whether or not the Chachamim applied the stringencies of the Torah to their decrees).

(R. Zeira citing Rabbanan): Really, Terumas Maaser of Demai should not have the fifth added; so why did they require it? It was a protective measure, as if he would not need to add the fifth, he would not treat it with sanctity.

Really, Maaser Sheni of Demai should have the fifth separated, so why didn't they do this? It was a protective measure, as if he would need to separate it, he wouldn't ultimately even separate Maaser Sheni at all.