Reference for Chullin 9:4
עוֹר שֶׁיֵּשׁ עָלָיו כַּזַּיִת בָּשָׂר, הַנּוֹגֵע בְּצִיב הַיּוֹצֵא מִמֶּנּוּ, וּבְשַׂעֲרָה שֶׁכְּנֶגְדּוֹ, טָמֵא. הָיוּ עָלָיו כִּשְׁנֵי חֲצָאֵי זֵיתִים, מְטַמֵּא בְמַשָּׂא וְלֹא בְמַגָּע, דִּבְרֵי רַבִּי יִשְׁמָעֵאל. רַבִּי עֲקִיבָא אוֹמֵר, לֹא בְמַגָּע וְלֹא בְמַשָּׂא. וּמוֹדֶה רַבִּי עֲקִיבָא בִּשְׁנֵי חֲצָאֵי זֵיתִים שֶׁתְּחָבָן בְּקֵיסָם וֶהֱסִיטָן, שֶׁהוּא טָמֵא. וּמִפְּנֵי מָה רַבִּי עֲקִיבָא מְטַהֵר בָּעוֹר, מִפְּנֵי שֶׁהָעוֹר מְבַטְּלָן:
When there is the size of an olive of flesh on a skin in one spot, any person who-touches the filaments proceeding therefrom, or the hairs on the skin which are opposite [and touch the said flesh], is unclean. If there were two pieces of flesh of the size of two half olives each, it pollutes by being carried, but not by the mere touching it. Such is the dictum of R. Ishmael, but R. Akivah holds "That they do not pollute either by being carried or touched," but he admits, "That if the size of two half olives were stuck on a skewer and moved, it is unclean." Why, then, does [R. Akivah], in respect to the skin, hold it to be clean? Because the skin prevents their contact.