It started with Tansy cakes. I had to ask myself 'Why would anyone eat anything so utterly disgusting in taste'?
Chrysanthemum Vulgare is a common perennial in British Isles and name Tansy is said to be derived from Greek 'athansia', meaning 'immortal'. Reasons suggested for this include fact that dried flower lasts forever or that it has a medicinal quality contributing to long life. Looking back to Greek literature, Tansy was given by Gods to Ganymede to make him immortal. In language of flowers gift of Tansy means 'Rejected address' - " I am not interested in you". Its strange taste, not unlike smell of 'mothballs' might have something to do with this.
Tansy certainly had a reputation as a vermicide and vermifuge (killing and dispelling intestinal worms) in middle ages. John Gerard wrote in his 17th century Herball:
"In Spring time are made with leaves here of newly sprung up, and with eggs, cakes of Tansies, which be pleasant to taste, and good for stomacke. For if any bad humours cleave there unto, it doth perfectly concoct them and scoure them downewards".
Tansy was a common kitchen garden herb for medicinal and culinary use, in place of expensive foreign spices such as nutmeg and cinnamon. It was used to flavour custard, cakes, milk puddings, omlettes and freshwater fish. In Ireland it was included in sausages called 'Drisheens'. Its use as a springtime 'cleanser' became ritualised into a part of Christian religious Easter traditions; "On Easter Sunday be pudding seen, To which Tansy lends her sober green."
The consensus on this much written about herb is that it was used at Easter to purify blood after lent. This consensus shows a problem though, in that in England plant does not show leaves until end of May - well after Easter. This is evidence of assimilation of natural 'self-medicating' herbalism into a controlling religious patriarchy.
Observation of wild and domesticated animals shows that they regularly self-medicate with wild plants. Sick chimpanzees chew bitter leaves from a bush not normally part of their diet, and then recover. Research by Michael Hoffman shows that a particular nematode worm is common in monkey's gut during rainy season and that their chewing of leaves coincided with prevalence of this parasite, which it destroyed. This was same bush that local tribes use to get rid of stomach parasites.
Dogs and cats self medicate by eating couch grass or cleavers. Parrots, chickens, camels, snow geese, starlings - all have been observed consuming substances normally alien to their diet to remedial effect. Bears particularly are venerated by North American Indian culture because they symbolise powers of 'regeneration'. North American Indians discovered use of a root called Osha from bears. It is so effective as an all round painkiller, antiviral, antipeptic that it is now on endangered species list.