אָדָם וְכֵלִים מִטַּמְּאִין בְּמֵת. חֹמֶר בָּאָדָם מִבַּכֵּלִים וְכֵלִים מִבָּאָדָם. שֶׁהַכֵּלִים שְׁלשָׁה וְהָאָדָם שְׁנָיִם. חֹמֶר בָּאָדָם, שֶׁכָּל זְמַן שֶׁהוּא בָאֶמְצַע, הֵן אַרְבָּעָה. וְשֶׁאֵינוֹ בָאֶמְצַע, הֵן שְׁלשָׁה: [Both] persons and vessels can be defiled through a corpse. A greater stringency applies to persons than to vessels and to vessels than to persons. For with vessels [there can be] three [series of defilements], whereas with persons [there can be only] two. A greater stringency applies to persons, for whenever they are in the middle of a [series] there can be four [in the series], whereas when they are not in the middle of a [series] there can be [only] three.Mishnah Oholot 1:4

אָדָם וּבְגָדִים מִטַּמְּאִים בְּזָב. חֹמֶר בָּאָדָם מִבַּבְּגָדִים, וּבַבְּגָדִים מִבָּאָדָם. שֶׁהָאָדָם הַנּוֹגֵעַ בְּזָב מְטַמֵּא בְגָדִים, וְאֵין בְּגָדִים הַנּוֹגְעִין בְּזָב מְטַמְּאִין בְּגָדִים. חֹמֶר בַּבְּגָדִים, שֶׁהַבְּגָדִים הַנּוֹשְׂאִין אֶת הַזָּב מְטַמְּאִין אָדָם, וְאֵין אָדָם הַנּוֹשֵׂא אֶת הַזָּב מְטַמֵּא אָדָם: Persons and garments can be defiled by a zav. A greater stringency applies to persons than to garments and a greater stringency applies to garments than to persons. For a person who touches a zav can defile garments, whereas garments that touch a zav cannot defile [other] garments. A greater stringency applies to garments, for garments which form the support of a zav can defile persons, whereas a person who forms the support of a zav cannot defile [other] persons.Mishnah Oholot 1:5