The Original use of Blood in Magic
Our ancestors were far more robust about killing and eating animals, and not just our pagan forebears by any means. Only in the last two generations in Ireland have we moved so far from the land and from the necessity of killing our own food, that we can turn up our noses in disgust at the killing of animals for food.: and only the very young have had en masse, no experience even of fishing, or skinning a rabbit on a scouting trip. The rather precious attitude we adopt toward death in general and inparticular towards our place in the food chain serves as an alarming symptom of our aloofness from nature and the natural world.*
Our ancestors hunted to live. The absence of game to supplement the diet was a disaster. It meant life or death to entire villages. The acts of landlords in enclosing commons and reserving stag & deer only for the aristocracy, right down to the more modern trick of hanging or transporting poachers was immoral and as unnatural as any you can imagine.When the peasant was cut off from his natural source of meat, when land became property, the right to hunt and kill game became the right to live and the right to decide who else should live. It was the beginning of the divorce between man and land and between socereignity and the land -it is almost beyond the modern imagination, a land where there are no state preserves, no royal forests, no great estates, just land, and forest, belonging to all....of course now, we need state preserves to maintain whats left of our natural world and protect it from our indifference. And those who hunt, hunt for sport, without respect or understanding and cause more damage in the process.
We take life, in order to nourish. We take life in order to give it as a gift. We propitiate the gods, spirits, elementals and ancestors with blood sacrifice.
From the comments of Tacitus and Ceasar to the discovery of bodies in the bogs of Europe and Ireland, people have argued about the existance of a cult of human sacrifice particularly among celtic societies. Was it propaganda, or accurate eyewitness reporting on the romans' behalf? Were the bog bodies, undoubtedly victims of violence ritually murdered or are they just the unfortunate and exceptional victims of extraordinary acts? The point is we don't know and until they discover the lost text "How to ritually slaughter your victim: a handbook for aspiring Druids" they'll never be sure. But there are from the literature of Ireland and from tradition, as well as from archaelogical evidence, certain things we can say about blood and pagan Ireland.
Animals were sacrificed, at wells, in groves, for individual and communal needs: the celts in particular valued and had affection for their livestock and did not lightly take animal life. The act of sacrifice, itself an inherently wasteful act as the meat is then taboo, represented a real emotional and financial investment for the petitioner. Animal sacrifice was for one of many reasons: the community hunted in the forest and therefore sacrificed one of their own animals periodically to propitiate the gods of the forest. This is also applicable theoretically to human sacrifice. The sacrifice of an animal when a large favour was needed from the gods or to bribe the Morrigan into taking ones side in battle, these were common reasons. To sacrifice dogs (and other animals)and send them to the otherworld with a warrior was common. To sacrifice and let blood onto the earth (whether animal or human, unclear) stakes a claim to the earth, and it is almost certain that after a battle, the prisoners of war were sacrificed in thanksgiving, in propitiation of the war furies and in order to show that the land (or property) gained by the war had now changed hands.
In magic and for magical purposes the use of blood was rarely to propitiate gods: however it was used to invoke gods, or spirits who are attracted by the life force in blood and used to bind the practitioner to the natural world so that they would not get lost in the otherworld during Imramma. The letting of blood was used in medicine and magic for similar purposes, to release the bad and relieve pressure. In magic the power of blood was harnessed to amplify a spell's power or to make a charms doubly effective, and to make curses lethal. As lead was used to bind curses thrown into wells, so blood was used to bind curses into the earth or that were to burn in the fire. Death was marked with the slaughter of animals and feasts often called for the wholesale slaughter of cattle and in return the letting of human blood was considered necessary.
Blood was used as: as magical ingredient in itself, just like a herb or a resin; a force like magic, ie life force, used to carry magical intention like a piggyback ; a binding element, binding the spell to a place, the practitioner to a place or time, the act of magic to a certain outcome; and of course the magical blood ties that have by tradition been seen as strong enough to transcend even death binding the witch to her clan and the clan to the witch. It was scrutinised in healing, used as a symbol of the body or mind, thought to be subject to humours and troubled by the spirit and energy of otherworldly creatures. the letting of it caould release troubles of the mind or heart, and of the body like fever.
*I do not include here those who give up meat in protest against unnnatural farming methods and animal welfare. I could never bring myself to sacrifice the morning rasher but I do realise how morally superior those who do are to me. (is that what you had in mind Liossa? can I stop grovelling now?)