(R. Yirmiyah citing R. Yaakov bar Acha citing R. Shimon ben Lakish): (When the Mishnah taught that according to R. Eliezer, if he separated more than one in ten, he should make it Terumas Maaser for produce elsewhere), R. Eliezer follows the view of Beis Shammai (earlier in Perek 1 Mishnah 2 - Chulin 56) that the Terumah there is in a state of Dimua (mixed together with the rest of the produce).

According to R. Yochanan (that in all cases, Beis Shammai's law applies that Terumah can be created in the form of Dimua), it is fine - 1/10th is sanctified as Terumah and as for the rest, 1/10th is Terumah and the rest is Tevel concerning its Ma'asros. Therefore, it was necessary for R. Eliezer to say, '(if he designates) more than (1/10th)' he should desiginate the excess as Terumas Maaser for produce elsewhere.

Question: But according to Chizkiyah, it is difficult - 1/10th that is sanctified as Terumah and as for the rest, 1/10th is Terumah and the rest is fully Tevel (even concerning its Terumah); but the Mishnah taught that '(if he designates) more than 1/10th, he should designate the excess as Terumas Maaser for produce elsewhere' - let him designate it as Terumah for produce elsewhere?

Answer: Chizkiyah follows R. Chiya's version of of Mishnah that actually says 'he should designate the excess as Terumah for produce elsewhere'.

What is R. Yishmael's source (to say in our Mishnah - Chulin 78(c) 2.) that a person may make up to half Chulin and half Terumah)? The pasuk states (Devarim 18:4), "The first of your grain'' - it's enough that you Terumah should be as your grain. What the source that he has done nothing unless he has left some behind? The pasuk states concerning separating Challah (Bamidbar 15:21), "from the first of your dough'' - but not all of the first.

(Mishnah): There are three times when the basket (used for measuring Terumah) is measured; (at the time of ripening of) the first fruits, the last fruits and the middle of the summer.

One who counts out (when he tithes, aside from the Terumah which may only be taken through estimation) is praiseworthy; one who measures is more praiseworthy; one who weighs out is the most praiseworthy of the three.

(Gemara) Question: (The Mishnah taught that one who counts out is praiseworthy.) Than whom?

Answer (R. Chuna): Than one who separates based on evaluation (without measurement).

(R. Chanina, son of R. Hillel): The Mishnah also indicates this, as it says that one who weighs out is more praiseworthy than the three. (This shows that there are actually four ways to separate).

Rebuttal (R. Chanina): It should be read as 'of the three', meaning that there are in fact only three ways.

(Mishnah) (R. Eliezer): Terumah is annulled in a mixture of 101.

(R. Yehoshua): In a little over 100, and the extra can be any amount.

(R. Yosi ben Meshulam): The extra is a Kav per one hundred Se'ah, meaning one sixth of the Se'ah that fell into the mixture.

(Gemara) Question: What's the source that Terumah is annulled in 101?

Answer (R. Yona): The pasuk states (Bamidbar 18:29), "From all your gifts, you shall separate every gift of Hash-m from its choicest portion, that part of it which is to be consecrated.'' This refers to Terumas Maaser, which is 1/100th of your produce (as it's 1/10th of the Maaser Rishon). The pasuk teaches that if it fell back into the rest of the pile (i.e. 99), it prohibits them; implying that if there was any more than 99, it would have become annulled.

(R. Eliezer): An additional Se'ah is required.

(R. Yehoshua): Any minimal addition is required.

(R. Yosi ben Meshulam): An additional Kav (1/6th of a Se'ah) is required.