Taharos, Chapter 2, Mishnah 5. This mishnah completes a short series that charts the levels of tumah in different categories of food, following the chain of impurity to see how many degrees it can travel and at which degree the food is finally clean. Each of these mishnayos ends with a food that has shed its tumah completely and may therefore be eaten together with a stew of kodesh. Here we come to kodesh itself, where the chain runs one degree longer than it does in terumah.
The mishnah opens: "harishon vehasheni vehashelishi shebakodesh, temei'im umetam'in." In kodesh, three full degrees are both tamei in themselves and capable of passing their tumah forward. Each of them renders the next item of kodesh that it touches impure, carrying the chain along another step.
Then: "harevi'i pasul velo metamei." A note on the text: the printed reading here is posel, that it disqualifies, but as in the previous mishnah the better girsa is almost certainly pasul. The mishnah is describing the fourth degree itself. Kodesh that has become a revi'i is pasul, disqualified food, but it is no longer active. It does not pass tumah on to anything else.
And the conclusion: "vehachamishi ne'echal binzid hakodesh." Kodesh that has reached a fifth degree carries no tumah at all, and so it may be eaten in a nezid hakodesh, a stew of kodesh.
It is worth pausing on what a fifth degree could even mean. Where in the Torah's system do we speak about a fifth level of tumah? By the para adumah. There we do reckon with a fifth degree, and accordingly, even where a fifth level of tumah is a live concern in the stew, kodesh that stands at the fifth degree may still be eaten with it, because fifth degree kodesh no longer bears any tumah of its own.
The shape of the chain in kodesh is therefore the same as in terumah, only stretched by one: three degrees that are tamei and transmit, a fourth degree that is disqualified but inert, and a fifth degree that is entirely free of tumah and may be eaten in the stew.