Found it from the horse's mouth, finally: "We rub our tubes with buckſkin". https://archive.org/details/experimentsobser00fran_0/page/17/mode/1up?q=%22We+rub+o

Found it from the horse's mouth, finally: "We rub our tubes with buckſkin". https://archive.org/details/experimentsobser00fran_0/page/17/mode/1up?q=%22We+rub+our+tubes+with%22 https://archive.org/details/experimentsobser00fran_0/page/17... Don't know where Randall get "silk" from.