Orlah, Chapter Two, Mishnah 5. Before us is a very short mishnah, whose entire content is the recording of an interesting opinion regarding the dispute we learned in the previous mishnah.
In the previous mishnah we learned that although leavening and seasoning have the power to create a prohibition beyond the usual ratios of nullification of one hundred and two hundred that apply to Terumah, orlah and kilei hakerem, a question arose as to the law of tumah: an impure item that causes leavening or seasoning - does it convey tumah in any amount whatsoever? On this point Beis Shammai and Beis Hillel disagreed:
Beis Shammai: Even with regard to tumah, a small and minute quantity that causes leavening or seasoning creates tumah.
Beis Hillel: The item conveys tumah only in the usual measure - the volume of an egg.
The wording of the mishnah:
"Dostai ish Kfar Yasma hayah mitalmidei Beis Shammai" - Dostai, a man from the village of Yasma, was one of the students of Beis Shammai.
"Ve'amar: shamati mi'Shammai hazaken she'amar: le'olam eino mitamei ad sheyehei bo k'beitzah" - He testified that he heard from Shammai the Elder himself that impure food does not convey tumah unless it has the volume of an egg, and this is the opinion of Beis Hillel.
In summary: Although Beis Shammai disagreed and ruled that the measure of an egg's volume is not required, nevertheless Shammai himself agreed with the opinion of Beis Hillel - anything that does not have the volume of an egg does not create tumah.