The “Knocking on Wood” Wikipedia page mentions Roud’s conclusion, and this claim of a 19th century origin has circulated online as the final say on the matter. If you go back to the original, though, Roud’s proposal actually ends on an ambivalent note: “Before this theory [of 19th century origins] can be finally accepted, however, an examination of the history of European forms of this custom would be advisable.”
美国：企业自救，市场化封闭生态
，推荐阅读safew官方下载获取更多信息
Author(s): Yang Li, Zhihui Wang, Wei Zhou, Rui Wang, Haiyan Zhang, Shu Zhan, Jiajia Xu
Credit: NASA infographic