8קוֹרַת בֵּית הַבַּד שֶׁעָשָׂה רֹאשָׁהּ הָאֶחָד כִּסֵּא אֵינוֹ מִתְטַמֵּא בְּמִדְרָס מִפְּנֵי שֶׁאוֹמְרִין לוֹ עֲמֹד וְנַעֲשֶׂה מְלַאכְתֵּנוּ. אֲבָל אִם קָבַע אֶת הַכִּסֵּא בְּקוֹרַת בֵּית הַבַּד הַכִּסֵּא מִתְטַמֵּא בְּמִדְרָס וְאִם דָּרַס הַזָּב עַל הַקּוֹרָה לֹא נִטְמָא הַכִּסֵּא. וְכֵן אִם קָבַע הַכִּסֵּא בְּקוֹרָה גְּדוֹלָה אוֹ עָשָׂה רֹאשׁ הַקּוֹרָה הַגְּדוֹלָה כִּסֵּא אֵין טָמֵא אֶלָּא מְקוֹם הַכִּסֵּא בִּלְבַד וּשְׁאָר הַקּוֹרָה טָהוֹר. וְכֵן הַדִּין בְּכִסֵּא שֶׁקְּבָעוֹ בַּעֲרֵבָה שֶׁהוּא טָהוֹר:
When one made a seat on one of the ends of a beam of an olive press, it is not susceptible to midras impurity, for if a person were to sit there, he would be told: "Stand up and let us do our work." If, however, a chair was affixed to the beam of an olive press, the chair is susceptible to midras impurity. Nevertheless, if a zav trod on the beam, the chair does not contract impurity. Similarly, if one affixed a chair to a large beam or made a chair at the end of a large beam, only the place of the chair itself is susceptible to impurity. The remainder of the beam is pure. The same law applies to a chair that is affixed to a kneading trough; it is pure.