Halakhah su Levitico 17:11

To be sure, although there is no reported case of fatality as a result of bone marrow donation, the removal of bone marrow is not entirely without risk. The risk to the donor is, however, limited to the hazard of general anesthesia.²⁷Until now, medical studies conducted in conjunction with bone marrow procedures have failed to uncover a linkage between donation of bone marrow and an increased incidence of either mortality or morbidity. In the unlikely event that further studies yield data pointing to the existence of such a causal connection the issues herein discussed will require reexamination. Nevertheless, it may be argued that the risks of general anesthesia in an otherwise normal and healthy person do not rise to the threshold of risk of which Halakhah takes cognizance.²⁸Cf., Ẓiẓ Eli‘ezer, XIII, no. 101, sec. 6, who rules that even donation of blood cannot be regarded as compulsory because of the attendant danger. A similar view is advanced by R. Moshe Dov Welner, Ha-Torah ve-ha-Medinah, VII-VIII, 311. An identical ruling, but without accompanying explanation, is reported in the name of the Brisker Rav, R. Yiẓḥak Ze’ev Soloveitchik, by R. Avigdor Nebenzahl in a letter to the editor, Assia, vol. 14, no. 1–2 (Elul 5754), p. 208. Rabbi Waldenberg, Halakhah u-Refu’ah, IV, 143, advances an additional, albeit fanciful, reason for his refusal to regard blood donations as mandatory. Citing the verse “For the life of the flesh is in the blood” (Leviticus 17:11), Rabbi Waldenberg argues that requiring the donation of more than a minimal amount of blood (the quantity of a revi‘it) is tantamount to requiring a person to surrender his life. Apart from the obvious objections that might be raised, that position is difficult to maintain in view of the fact that the Talmud regards bloodletting as therapeutic and beneficial in preserving health. Cf., Iggerot Mosheh, Ḥoshen Mishpat, II, no. 103.

I have already written what I think on the level of the simple understanding about forbidden foods, in the prohibitions of the 'torn' [animals] (Sefer HaChinukh 73) and of forbidden fat (Sefer HaChinukh 147). But it is also possible to say about blood that besides the bad constitution [that it brings] - as it is of bad constitution - there would be in its eating a little acquisition of the trait of cruelty. As a man swallows from living beings, like him in the body, that thing in them that life is actually dependent upon and to which their spirit is connected. As it is well-known that beasts have spirits, which the wise men call a living spirit, meaning to say it is not an intelligent spirit. We can also see that their spirits have that aspect to guard from falling into one of the traps, and in a few other things. And Ramban, may his memory be blessed, wrote (Ramban on Leviticus 17:11) about the reason of blood, that it is well-known that that which is eaten returns to (dwells within) the body of the eater. And [so] if a man eats blood, there will be density and coarseness in the spirit of the man, just like the beast is dense and coarse. And he further wrote similar to that which I said, myself - that is not fitting for a spirit to eat a spirit.

And [of] the blood that is forbidden by Torah writ, there is some the prohibition of which is with excision and some with a negative commandment. Lifeblood is with excision - as in the place that excision for blood comes in the Torah, there it is stated life (literally, spirit), as it is stated (Leviticus 17:11), "For the life of the flesh is in the blood." But the prohibition of that which is not lifeblood, but rather the blood of the limbs is only with a negative commandment - since about it is it stated (Leviticus 7:26), "And any blood you shall not eat." And therefore they, may their memory be blessed, elucidated and said (Keritot 22a) that we are liable for excision with the blood that comes out at the time of slaughter, stabbing or decapitation, so long as it has redness in it; with blood stored in the heart; and blood that is let, so long as it flows and comes out - as it too is lifeblood, and therefore we are liable for it. And specifically flowing - to exclude the dripping at the beginning of the letting and at its end, which is not lifeblood, such that we are not liable excision [for it]. And so [too,] the concentrated blood - meaning to say the blood that oozes a little at a time at the time of slaughter, after the pouring blood came out; and so [too,] the blood of the limbs, such as the blood of the spleen, the blood of the kidneys, the blood in the testicles and the blood that lodges in the heart at the time of slaughter - we are not liable excision for it, but rather lashes. And that is when he eats a kazayit of it.