Yoso-tama-no-kakehashi; the first Japanese guidebook on raising rats

During the 18th century, raising the "nezumi" rodent became so prevalent in Japan that two guidebooks were published on the topic. The first guidebook was entitled Yoso-tama-no-kakehashi (1775) and the second was entitled Chinganso-date-gusa (1787). It remains unclear in these texts whether the term nezumi was used to refer to the rat (Rattus norvegicus) or the mouse (Mus musculus). In this review, I explore Yoso-tama-no-kakehashi (English translation: A bridge to obtaining novel jewel-like nezumi). It was written by the owner of "Shunpo-do" and comprises two volumes; the first is 34 pages in length and the second is 14 pages. It introduces the nezumi and then provides details on novel varieties and the methods that were used to raise them. The nezumi dwells in peoples' homes. It is noteworthy that the "norako" species is classified in the same group as the nezumi. The norako is smaller than the nezumi. Its alias is "hatsuka-nezumi", a term which is still used in Japan today when referring to the mouse. This indicates that when the guidebook was written people distinguished the rat from the mouse by identifying the rat using the word nezumi and the mouse using the word norako. Moreover, I recently confirmed that the rat varieties which are introduced in Yoso-tama-no-kakehashi, such as "white", "spotted", "black bear-like", "deer-spotted", and "cracked-mark", can be found in modern laboratory rats. Taken together, it is very likely that the term nezumi is used to refer to the rat in Yoso-tama-no-kakehashi and that this was indeed a guidebook on the rat.