Reference for Chullin 243:16

מפני מה ר"ע מטהר בעור מפני שהעור מבטלן:

But this would be obvious? - No, for you might have thought that R'Akiba maintains his view only where the knife cut it away, but where it was torn away by a wild beast he would concede that it is not rendered negligible; he therefore teaches us that the reason for R'Akiba's view is because the hide renders it negligible, making thus no difference whether it was torn away by a wild beast or cut away by the knife, for so it reads in the last clause: 'Wherefore does R'Akiba declare him clean in the case of the hide?

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