 Although the Cantong qi forever changed the history of Daoist alchemy, by no means are all Waidan works written in the Tang period (7th-9th centuries) inspired by its doctrines (Sivin 1968; Needham 1976: 132–74). During this period, however, Waidan methods increasingly tend to mirror features of the cosmological system (Sivin 1976 and 1980).