Reference for Kelim 20:1
הֲרֵי אֵלּוּ טְמֵאִים מִדְרָס. הַקְּלוּסְטָר, אַרְבָּעָה קַבִּין, הַתּוּרְמֵל חֲמֵשֶׁת קַבִּין, הַכְּרֵיתִית סְאָה. הַחֵמֶת שֶׁל שִׁבְעַת קַבִּין, רַבִּי יְהוּדָה אוֹמֵר, אַף הָרִבְצָל וְהַמִּזְוָדָה כָּל שֶׁהֵן, הֲרֵי אֵלּוּ טְמֵאִין מִדְרָס. וְכֻלָּם שֶׁנִּפְחֲתוּ, טְהוֹרִים, מִפְּנֵי שֶׁבָּטַל הָעִקָּר, וּבָטְלָה הַטְּפֵלָה:
Pillows, bed coverings, sacks and packing cases that were damaged are still susceptible to <em>midras</em> impurity [transmitted by sitting or lying]. A fodder-bag that can hold four <em>kav</em>, a shepherd's bag that can hold five <em>kav</em>, a traveling bag that can hold a <em>se'ah</em>, a skin that can hold seven <em>kav</em>, Rabbi Yehudah adds: also a spice-bag, and a food wallet that can hold the smallest quantity are susceptible to <em>midras</em> impurity. If any of them was damaged it becomes pure, since if the primary function is annulled, the secondary function is also annulled.