Bencao gangmu
The "Nihon Kokugo Daijiten" (2001) defines "chūgi" 籌木 or "chū" 籌 as "chips of wood anciently used instead of toilet paper", and cites the earliest recorded usage of "chūgi" ちうぎ in Ono Ranzan's 小野蘭山 (1847) "Jūtei honzō kōmoku keimō" 重訂本草綱目啓蒙 "Illuminated Compendium of Materia Medica". Modern Japanese dialect pronunciations of "chūgi" include "chyōi" or "chūge" in Hida (region) and "tsū" in Iwate Prefecture.