Taharos, Chapter 1, Mishnah 9. With this mishnah we bring the first chapter of Taharos to a close, and it closes with one of the more demanding cases in the chapter: loaves whose hollows are filled with water, and what happens when a sheretz touches the first loaf in a row of them.
The mishnah begins: "Kikar haKodesh shebesoch kumteih mayim mukdashim." The authorities differ over the exact metzius, the physical picture, of this case. We will follow the primary explanation of the Bartenura: we are dealing with loaves of kodesh, and each loaf has a cavity or depression in it, and that cavity holds water which is itself kodesh.
Before working through the case we need two pieces of background. The first is the ladder of degrees that we have been building all chapter. Chullin can descend only as far as the second degree; terumah can descend as far as the third degree; kodesh can descend all the way to the fourth degree. That difference is the engine of this entire mishnah.
Two rules about liquids
The second piece of background is actually a principle we will only reach formally later, in the second chapter, but without it this mishnah cannot be understood: the peculiar behavior of liquids. By rabbinic decree, a liquid that contracts tumah always leaps to the status of a rishon, a first degree, no matter what made it tamei. If chullin of the second degree touches chullin liquid, that liquid does not become a third degree (which in chullin would be nothing at all); it becomes a rishon. If terumah of the third degree touches kodesh liquid, that liquid becomes a rishon.
The second half of the rule is the limitation. If the solid food in question has already "maxed out" its ability to convey tumah, it cannot convey tumah to liquid either. Take terumah that has reached the third degree. Were it to touch another piece of terumah, nothing would happen, since terumah cannot descend past the third degree. Since that solid is powerless against another solid, it is equally powerless against liquid, and the rabbinic leap to rishon never gets started. In short: any food that could not render another solid tamei will not render a liquid tamei, even if the arithmetic would otherwise work out.
The case of kodesh: kulan tmeios
Let us come back to the loaves. Picture a line of kodesh loaves resting against one another, each one holding water in its hollow, and that water is kodesh as well, so it too can be brought down as far as a fourth degree. "Nitmeis achas meihen basheretz, kulan tmeios": the loaf at the head of the row is touched by a sheretz, which is an av hatumah. That loaf turns into a rishon, and so does the water sitting in its hollow. Loaf number one is in contact with loaf number two, so loaf two receives sheini status, while the water inside loaf two leaps up to rishon. Loaf two then touches loaf three: judging by the loaf by itself, loaf three would stand at the third degree, but the water in its hollow has already jumped to rishon, and that water raises its own loaf back up to sheini. As soon as that loaf meets the next one in line, the identical process starts over. The chain keeps feeding itself, and nothing exists to bring it to a halt. So from that single contact of the sheretz with the loaf at the front, kulan tmeios, not one loaf in the row escapes tumah.
The case of terumah: metamei shnayim uposeil echad
The mishnah goes on: "Biterumah, metamei shnayim uposeil echad." When the loaves are terumah, the self-feeding chain breaks, and we can pinpoint exactly where. The av hatumah makes contact with loaf one: that loaf is a rishon, and the water in its hollow is a rishon too. Loaf one meets loaf two, which takes on sheini status, and the water in loaf two's hollow springs to rishon, but the loaf is already at the second degree and stays there. Now loaf two touches loaf three. Leave the water out of the reckoning for a moment and consider the loaf on its own: it stands at the third degree. Terumah at the third degree is pasul and may not be eaten, yet it has no strength to pass tumah along to any other terumah. And a food that cannot affect solids cannot affect liquid either, so the terumah water in that third hollow remains entirely tahor. With no rishon water in hollow number three, nothing drives the sequence any further. That is metamei shnayim uposeil echad: two loaves turn tamei with the power to transmit onward, while the third is merely disqualified and no more.
When the liquid is shared: mashkeh tofeiach
The mishnah's final clause: "Im yeish beineihem mashkeh tofeiach, af biterumah hakol tamei." If between the loaves there is moisture, a mist or dripping wetness, then the liquid is no longer sealed inside the cavity of one individual loaf; it is shared among them. In that situation, even with terumah, which we just saw is the more lenient case, everything becomes tamei. The connective liquid restores the endless recursion, and the whole row goes down.
That brings the opening chapter of Taharos to completion. It is worth pausing to appreciate what you now hold in hand: the graded scale of degrees, the unusual rules that govern liquids, and the boundaries of a food's ability to transmit tumah are the instruments we will keep drawing on from here onward.