Terumot, Chapter Four, Mishnah Eight
Our mishnah deals with the issue of whether the kind of terumah that fell into the hullin (non-sacred produce) must be exactly like all of the hullin into which it fell.
1) Rabbi Joshua says: black figs can bring up white ones, and white ones can bring up black ones.
a) In the case of cakes of figs, the large can bring up the small, and the small can bring up the large.
b) Round cakes of figs can bring up square cakes, and square cakes can bring up round ones.
2) Rabbi Eliezer prohibits this.
3) Rabbi Akiba says: if the kind which fell in is known, then the one kind cannot bring up the other kind, but if the kind is not known, the one kind can bring up the other.
Section one: According to Rabbi Joshua if a black terumah fig fell into a pile of 100 hullin figs, fifty of which were white and fifty black, the owner can remove one fig, give it to the priest and eat the rest. Even though it is clear that the fifty white figs were not the terumah fig that fell in, so that in reality there are only fifty-one figs that could have been the terumah fig (the fifty one black figs), the white figs can join with the black figs to make up the required 100 to 1 ratio. Rabbi Joshua goes on to the say that the same is true if a large cake of figs fell into a pile of small and large cakes of figs, or if a round cake fell into a pile of round and square cakes. Since they are all figs, they all join to create the required ratio to bring up the terumah figs.
Section two: Rabbi Eliezer forbids this for the reason that I explained abovein this scenario only fifty-one of the figs is potentially terumah and therefore we dont have the required 100-1 ratio.
Section three: Rabbi Akiva mediates between their two opinions. If we know that a white fig fell in, then only white figs can count to the ratio of 100-1. But if we dont know which color fig fell in, then all of the figs could have been terumah and we will have the required ratio. It seems that conceptually Rabbi Akiva agrees more with Rabbi Eliezer, but that he notes that if we dont know exactly what fell in, then it doesnt matter what color the figs are, as long as there is a 100-1 ratio.