Jewish ultra-Orthodox concern with blood infusions is in part superfluous. Jews are enjoined against consuming animal blood, “for its soul is in its blood.” Soul, however, can be only in a single place at a time, and it’s either in the animal or in its blood. The commandment, therefore, only deals with slain animals and leaves open the possibility of drawing blood from live animals and humans.
There is an adjoining prohibition against cutting flesh of a living animal. Blood, however, is not flesh: we’re allowed to eat animal flesh but not its blood. In light of the “soul-blood” commandment, we can plausibly infer the prohibition of shedding blood of a living animal until it dies. It is doubtful whether we can extend the prohibition of cutting flesh onto all animal suffering: doubtlessly, a sheared sheep suffers considerably, but shearing is not regulated. Perhaps, it is prohibited to inflict the enormous, death-like suffering only.
Drawing blood of live humans and animals by medical means doesn’t cause them considerable suffering or connected with their death, so is not prohibited.
Perhaps blood consumption is prohibited per se, regardless of the blood’s source? Capital punishment for intercourse with menstruating women favors such a wide assumption.
A contrary argument, that priests and arguably medical professionals, though in constant contact with blood, incur no guilt on its account, would be wrong. They derive no personal benefit from the blood and are not culpable. True, doctors receive payment for their services, but the payment is for healing; the contact with blood remains circumstantial.
The blood of menstruation, however, is considered the one from wound, therefore symbolical of death. Plausibly, the blood not related to wound and death, such as drawn for infusion, lacks the stigma.
There is also an argument of necessity. Animal slaughterer gets in touch with blood but is not guilty because the contact is unavoidable. Blood infusion in life-threatening circumstances can be justified by similar necessity as that which makes us slaughter the animals to eat and live ourselves.
The example of woman in childbirth is instructive. During the birth, she becomes unclean through the contact with blood of the wound, and is instructed thereafter to purify herself by moderate sacrifices. I lean to the opinion that blood transfusion from living humans and animals is possible but leads to the receiving party’s ritual impurity.
