7Gregory, Isabell Augusta (Persse). Gods and Fighting Men. London: J. Murray, 1904. 306-09.
This book may be read in its entirety here.
This story is not one of the earlier elements of the Fenian Cycle; it is likely of late medieval origin. However Fionn's ability to use his magical powers to recover treasure is mentioned in an eighth century text. In another version of this story the antidote, in addition to restoring Fionn's youth, also gives him wisdom. (Ó hÓgáin, Dáithí. Fionn Mac Cumhaill: Images of the Gaelic Hero. Dublin: Gill and Macmillan, 1988. 23, 134.)