A long, long time ago, before there was a Talmud and rabbis, there were Priests and there was a Temple. The Priests maintained a state of holiness by rigidly policing the grounds of the Temple to prevent contaminants from proliferating. In the daf beginning today, the rabbis study the laws of disposing of contaminated materials with the goal of applying them to the disposal of chametz.
Daf 337 (Pesachim 14a-14b)
Mishnah. Materials contaminated to different degrees were permitted to be burned together in the Temple, although it added a “degree” of contamination to the less contaminated components. R’Meir derives from this that both contaminated and uncontaminated chametz may be burned together on the eve of Pesach. R’Yose, R’Eliezer, and R’Yehoshua all agree, although they disagree on a related issue (commingling Terumah for burning).
Gemara. The gemara seeks to determine by what degree of contamination commingled products are augmented.