Taharos, Chapter 8, Mishnah 9. This is the closing mishnah of the chapter, and it takes up a question that runs through much of the laws of tumah and taharah: what counts as a real connection between one body of liquid and another? When two liquids touch, is that enough for tumah to travel from one to the other, or for the taharah of a mikveh to reach into the other? The Mishnah presents a machlokes and then lays down a rule.
Picture a stick, a walking staff or something similar, saturated through and through with liquid that carries tumah: "Makel shehi mele'ah mashkin temei'in". Now, "keivan shehishikah lamikveh", its end is brought up against the water of a mikveh. The verb hishikah shares its root with neshikah, a kiss, and the image is precise: the tip of the staff does no more than graze the surface of the mikveh's water.
The mikveh, of course, is the great instrument of taharah. And so the ruling: "Tehorah", the entire stick, meaning the whole of the liquid absorbed in it, becomes tahor, "divrei Rebbi Yehoshua", these are the words of Rebbi Yehoshua. In his view, the taharah of the mikveh reaches through the point of contact and up along the length of the stick, so that if the stick were afterward to touch something susceptible to tumah, it would transmit nothing.
What stands behind Rebbi Yehoshua's position is a principle: a katfres, liquid lying along an incline or a slant rather than gathered together on one level, is nonetheless treated as a genuine connection.
"Vachachamim omrim: ad sheyatbil es kulah." The Chachamim disagree. A kiss at the tip accomplishes nothing; the stick becomes tahor only when the whole of it is immersed in the mikveh. For the Chachamim, a slanting connection is simply not a connection.
The Rule
Now the Mishnah generalizes into a rule. Three forms of liquid contact are named, "hanitzok vehakatfres umashkeh tofe'ach", and of them the Mishnah declares "einan chibur": they do not constitute a joining, not where tumah is at stake and not where taharah is at stake.
Nitzok is a poured stream, an unbroken column of liquid running from one vessel into another; picture water poured straight into a kettle. Katfres is the slanting flow we have just described. Mashkeh tofe'ach is mere dampness, dripping moisture, liquid that is not continuous but broken. (Some understand katfres umashkeh tofe'ach as a single item set opposite nitzok, so that the Mishnah lists two categories rather than three. Either way, the halachah is the same.)
All of these are the kinds of contact that we would instinctively call thin or partial connections, and the Chachamim hold that halachah sees them the same way. And they are consistent about it: "lo latumah velo lataharah", such a link neither carries tumah across nor carries taharah across. It cuts both ways. One cannot make something tahor through it, and one cannot make something tamei through it either.
"Veha'eshboren chibur latumah velataharah." An eshboren is a hollow that holds a standing pocket of water, such as a small cavity in the wall or side of a mikveh where water collects. Because the water there sits together as one body rather than sloping or trickling, it is a full chibur, effective both for tumah and for taharah.
With this, Chapter 8 comes to a close.