Mishnah Mikvaos 10:8: If one ate impure foods or drank impure liquids [other than water], and immersed, and vomited them out, they [the liquids] are impure because they are not [rendered] pure in the body [as one immerses]. If one drank impure waters, and immersed, and vomited them out, they [the waters] are pure because they are [rendered] pure in the body. If one swallowed a pure ring, and entered a tent containing a dead body [thereby rendering himself impure], and was sprinkled [with the chatat waters as part of the purification process], and was [then sprinkled] a second time, and immersed, and vomited it out, it thereby is as it was [i.e. the ring remains pure, since swallowed items are not rendered impure, and the body had already been purified once it was vomited out]. If one swallowed an impure ring, he may immerse and then eat terumah [that evening, and is not rendered impure by the swallowed item]. If he vomited it out, it is impure, and it has rendered him impure. Regarding an arrow stuck into a person, at times when it can be seen [sticking out of the body], it interposes [and prevents one from having a fully valid immersion]; but at times when it cannot be seen, one may immerse and then eat his terumah [that evening, and the arrow is not considered an interposition preventing an effective immersion].

אָכַל אֳכָלִים טְמֵאִים, וְשָׁתָה מַשְׁקִים טְמֵאִים, טָבַל וֶהֱקִיאָן, טְמֵאִים, מִפְּנֵי שֶׁאֵינָן טְהוֹרִים בַּגּוּף. שָׁתָה מַיִם טְמֵאִים, טָבַל וֶהֱקִיאָם, טְהוֹרִים, מִפְּנֵי שֶׁהֵם טְהוֹרִים בַּגּוּף. בָּלַע טַבַּעַת טְהוֹרָה, נִכְנַס לְאֹהֶל הַמֵּת, הִזָּה וְשָׁנָה וְטָבַל וֶהֱקִיאָהּ, הֲרֵי הִיא כְמוֹת שֶׁהָיְתָה. בָּלַע טַבַּעַת טְמֵאָה, טוֹבֵל וְאוֹכֵל בַּתְּרוּמָה. הֱקִיאָהּ, טְמֵאָה וְטִמְּאַתּוּ. חֵץ שֶׁהוּא תָחוּב בָּאָדָם, בִּזְמַן שֶׁהוּא נִרְאֶה, חוֹצֵץ. וְאִם אֵינוֹ נִרְאֶה, טוֹבֵל וְאוֹכֵל בִּתְרוּמָתוֹ:

Mishnah Niddah 1:1: Shammai says: For all women, their hour [of discovering menstrual blood] suffices [to reckon the period of their impurity from that moment]. Hillel says: [the period of impurity is reckoned retroactively] from [the previous] examination to [the latest] examination, even for many days [i.e. she is assumed to have been impure the entire time]. The Sages say: [the law is] not according to this one nor according to that one, but rather [the period of impurity is reckoned] from that time to that time [on the previous day, i.e. twenty-four hours earlier, when this] lessens [the period] from examination to examination; and [it is reckoned] from [the previous] examination to [the latest] examination [when this] lessens [the period] from that time to that time [on the previous day, twenty-four hours earlier]. For any woman who has a regular cycle, her hour [of discovering menstrual blood] suffices [to reckon the period of her impurity from that moment]. And if a woman uses checking-cloths [literally: witnesses, to clean herself before and after intercourse], this is thereby like an examination, and it lessens [the period of impurity] from [being measured from] that time to that time [i.e. twenty-four hours earlier], or from [the previous] examination to [the latest] examination.

שַׁמַּאי אוֹמֵר, כָּל הַנָּשִׁים דַּיָּן שְׁעָתָן. הִלֵּל אוֹמֵר, מִפְּקִידָה לִפְקִידָה, וַאֲפִלּוּ לְיָמִים הַרְבֵּה. וַחֲכָמִים אוֹמְרִים, לֹא כְדִבְרֵי זֶה וְלֹא כְדִבְרֵי זֶה, אֶלָּא מֵעֵת לְעֵת מְמַעֵט עַל יַד מִפְּקִידָה לִפְקִידָה, וּמִפְּקִידָה לִפְקִידָה מְמַעֶטֶת עַל יַד מֵעֵת לְעֵת. כָּל אִשָּׁה שֶׁיֶּשׁ לָהּ וֶסֶת, דַּיָּהּ שְׁעָתָהּ. וְהַמְשַׁמֶּשֶׁת בְּעִדִּים, הֲרֵי זוֹ כִפְקִידָה, וּמְמַעֶטֶת עַל יַד מֵעֵת לְעֵת וְעַל יַד מִפְּקִידָה לִפְקִידָה: