(Mishnah - R. Yosi): One is liable for offering outside the Mikdash only on a Mizbe'ach.

(Rav Huna): He learns from "va'Yiven No'ach Mizbe'ach la'Shem" (i.e. even Ha'alas Chutz requires a Mizbe'ach).

Avodah Zarah 28b: Shmuel taught that one may apply a potion to an eye about to leave the socket on Shabbos, because nerves connect the eye to the heart.

Bava Kama 84a (Tana d'Vei Chizkiyah): "An eye for an eye, a soul for a soul", but not an eye and a soul for an eye;

If Beis Din inflicted bodily damage, they would blind the eye of one who blinded an eye. Sometimes this would kill him, and he lost his eye and his soul for an eye!

90b (Mishnah): Once, R. Akiva obligated a man to pay 400 Zuz for uncovering a woman's head in the market. The man brought witnesses who saw her uncover her hair to dab some oil into her hair.

R. Akiva: One may not injure himself, but if he does, he is exempt. Others may not injure him, if they do, they are liable.

Shabbos 129a (Rav and Shmuel): If one let blood, he should not sit in a windy room. This can endanger him!

129b: If one lets blood and immediately stands up, he is closer to death than life.

(Shmuel): Monday and Thursday are bad days for bloodletting, unless he wants to rely on merits of his ancestors.

It is good to drink immediately after bloodletting, and to eat after the time to walk half a Mil (nine or 11 minutes).

We do not know whether eating more or less than the given time afterwards is bad, or just ineffective.

Rambam (Hilchos Rotze'ach 1:14): Anyone who could save (someone being pursued), but did not, transgressed "Lo Sa'amod Al Dam Re'echa."

Kesef Mishneh: Hagahos Maimoniyos says that the Yerushalmi (Terumos 8:4) concludes that one must enter Safek danger to save another. It seems that this is because the other is in definite danger.

Bach (CM 426:2): The Beraisa connotes that even if it is a Safek if he will save, he must enter Safek danger to try. However, the Rambam's words 'he could save' connote that that surely he can save. The Tur says 'and the Rambam says...', for he rules unlike this.

Sefer Chasidim (674): "Lo Sa'amod Al Dam Re'echa", but if many are fighting against Ploni, do not enter the battle. Do not try to save a heavy person who is drowning, lest you drown with him.

Me'iri (Bava Kama 91b): One may not harm himself, for it says "v'Ach Es Dimchem l'Nafshoseichem Edrosh." This is only an Asmachta.

Mishneh Halachos (4:245): The Mishnah forbids harming one's own body. Tana'im argue about this. The Rif, Rambam and Rosh forbid. The Tur (CM 420) brought the Ramah, who permits. The Beis Yosef supported this. Many forbid mid'Oraisa. The Me'iri says that the verse is only an Asmachta. Some say that we do not learn from before Matan Torah. However, we find that we do! We learn from Rivka that a virgin gets a year to prepare for Chupah (Kesuvos 57b), from Sarah that we wait 10 years for a woman to give birth (from when she comes to Eretz Yisrael - Yevamos 64a), and from No'ach (that even offering outside the Mikdash requires a Mizbe'ach). Since most Poskim rule like the Rambam, one may (wound himself to) give blood only if it will heal himself, or a dangerously sick Yisrael needs the blood. Further, one cannot authorize another to wound him to take blood from him. The Maharshal forbids wounding oneself for naught. The Mishnah forbids even for monetary gain. It is especially improper to give blood (in Chutz la'Aretz), for presumably a Nochri will receive it.

Shulchan Aruch (CM 426:1): If Reuven sees Shimon drowning..., and Reuven himself could have saved him or hired others to save him, but he did not, he transgressed "Lo Sa'amod Al Dam Re'echa."

SMA (2): Hagahos Maimoniyos obligates entering Safek danger to save another in definite danger. Perhaps the Shulchan Aruch and Rema omitted this because the Rif, Rambam and Rosh did not bring it.

Radvaz (3:627 (1052), cited in Mishbetzos Zahav OC 328:7): If a lord told Reuven 'let me cut a non-vital limb from you, or else I will kill Shimon', some say that Reuven must forfeit the limb. One may cure an eye on Shabbos due to mortal danger. Piku'ach Nefesh overrides Shabbos, but Shabbos overrides a non-vital limb. All the more so Piku'ach Nefesh overrides a limb! I say that this is mere Midas Chasidus. The Kal va'Chomer is invalid. Danger to a limb does not override Shabbos, for it is an Ohnes from Shamayim. This is no source to obligate putting Ohnes upon oneself to help another. Also, one could bleed to death from cutting off a limb. I saw a man die from mere scratches on the ear to draw blood. Who says that another's blood is redder than yours?! Also, the limbs must observe Shabbos - "one will live in them (Mitzvos)", he will not die in them. If not for this verse, even mortal sickness would not override Shabbos. One need not sacrifice himself to save another. One must use his money to save others, but he need not endanger his limbs. Further, we do not punish due to a Kal va'Chomer. Losing a limb is the ultimate punishment. It is harsher than lashes. We do not literally fulfill "an eye for an eye... a burn for a burn", lest he die. There is more mortal danger from cutting off a limb than from a burn! Also, "its ways are pleasant" - it is illogical that one must forfeit his eye, hand or leg to save another. It is Midas Chasidus; happy is one who can fulfill this. If it is mortal danger, he is a crazy Chasid. The Safek of his life overrides the certain death of his friend.

Shach (YD 157:3): If there is risk to a limb if one will not transgress a Lav, perhaps this is like loss of money (and one may not transgress), or like loss of life (one may transgress). It seems that we are lenient.

Divrei Yatziv (32): The Rikanti (470) brings that some obligate forfeiting a limb to save another's life. They learn from danger to an eye. It overrides Shabbos only because there is danger, but another limb would not.

Hagahos Rema (on Mordechai Sof Sanhedrin 718, from Arugas ha'Bosem): If a Nochri said 'cut off Ploni's hand. If not, I will kill you', R. Baruch permits cutting it for Piku'ach Nefesh. He must pay to Ploni the value of his hand. We are Mechalel Shabbos for a limb, due to mortal danger. If Beis Din would remove an eye, perhaps this would kill (Bava Kama 84a). Even though usually it does not kill, we do not follow the majority regarding Piku'ach Nefesh.

Igros Moshe (CM 1:103): Perhaps donating blood (when no patient needs it now) is forbidden, even if one is paid for this, for it harms oneself. Tosfos (Bava Kama 91b DH Ela) forbids harming oneself even for profit. However, we learned from a Nazir, who is called a sinner for paining himself. If he does so willingly for profit, he is not pained! We can distinguish. The pain of refraining from wine is only if he desires it. If one desires the profit more, he feels no pain. Bodily harm is always painful. However, the Gemara calls bloodletting a Refu'ah. Nature has changed since then; the Rambam (Hilchos De'os 4:18) counsels to let blood less often than the Gemara says. Even though we do not let blood nowadays for Refu'ah, presumably nature has not changed totally and even nowadays it helps a bit. Therefore, we do not protest if one donates blood.

Chelkas Yo'av (Dinei Ohnes 7, cited in Shevet ha'Levi 5:219): Just like one need not endure pain for the Mitzvah of Sukah, one need not endure sickness or great pain for any Mitzvah. We learn from Sukah 26a. Rava exempts from Sukah due to pain. We challenged him from the Mishnah, which exempts (only) due to illness. The Mishnah exempts when rain falls. Surely this is due to pain! What was Rava's Chidush, and why did we challenge him? We must say that one is exempt from a Mitzvah if it will cause illness without danger. Great pain is like illness without danger. Rava taught that even small pain exempts.

Rebuttal (Shevet ha'Levi): Rashi says that the Mishnah exempts from a 'side' Ohnes (rain). Rava exempt when sitting in any Sukah would pain him (due to wind, flies...) Rishonim say that the exemption of Sukah is due to "Teshvu" - the wall you dwell. R. Mano'ach (Hilchos Sukah 6:2) explicitly says that the exemption due to pain or illness without danger is only for Sukah. Maharam Shik (OC 260) obligates even for the Mitzvah mid'Rabanan of the four cups of wine, even if he will get sick without danger. The Mishnah Berurah exempts in such a case, but only because free men do not drink like this.

Shevet ha'Levi (ibid.): If one has a rare blood type and needs much blood, if another could donate, but refuses due to the pain, toil or fear, does he transgress "Lo Sa'amod Al Dam Re'echa"? The Radvaz holds that forfeiting a limb to save another is only Midas Chasidus. If there is danger, it is lunacy, i.e. if the danger is like an even Safek. If there is a very small danger, and there is at least an even Safek of saving the person, it is Midas Chasidus. Donating a moderate amount, like the amount that bloodletters used to take, is not considered dangerous. Even though nowadays most do not let blood, we see that donating is not dangerous. Surely, it is a Mitzvah to donate. Sometimes they extract all a person's blood over several hours in order to get blood cells. This entails danger. Surely there is no obligation to do so. If it is only a small danger, one may do so for Midas Chasidus.

Tzitz Eliezer (16:23): I say that "Nefesh ha'Basar b'Dam Hu" teaches that life depends on blood. A Revi'is of blood is the Shi'ur of human life. Surely, one need not donate more than this for any Mitzvah, except for the three that obligate Mesiras Nefesh. Shabbos 129 shows that letting blood is dangerous. Even though we know how to recover from it, it is called dangerous. We say that one is mortally sick even if we know a cure. People let blood to avoid a greater danger. Today we do not do so due to the danger of those who let blood. Sometimes people faint even when a small blood sample is taken for tests! If one with a rare blood type wants to give more than a Revi'is, if he feels that it will not harm him, this is Midas Chasidus. In Sanhedrin 73a, an extra verse teaches that one must even toil to hire others to save a life. Without the verse, he would be exempt. There is no source to obligate giving one's blood. Yad Ramah (there) says that one need not even spend his money to save another! Surely one need not endanger himself to save another. Perhaps it is forbidden.

Shulchan Aruch ha'Rav (Hilchos Nizkei Guf v'Nefesh 7): Some obligate entering a Safek danger in order to save another from certain death. Some disagree. We are lenient about Safek Nefashos.

Divrei Yatziv (CM 79:31): If giving blood will merely pain or weaken a person, even if he will be bedridden for a day or two, if there is no concern for danger, he must endure the pain to save another's life. If one can buy blood, this is like the obligation to hire people to save a life. If there is danger, the Poskim rule unlike the Yerushalmi; one need not endanger himself. In Hilchos Shabbos (329:8) Shulchan Aruch ha'Rav wrote that if a boat with Yisre'elim is sinking, one should not endanger himself to save others, since he himself is not in danger. Even though he is in Safek (if he tries saving) and the other will surely die (if he does not save him), "va'Chai Bahem" - do not risk your life for the Mitzvah of "Lo Sa'amod Al Dam Re'echa." Keneses ha'Gedolah (Hagahos ha'Tur 425) says that one should not endanger himself to try to save someone being pursued. Chikekei Lev (CM 26) says that since the pillars of Hora'ah, the Rif, Rambam, Rosh and Tur, did not bring the Yerushalmi, and even though the Beis Yosef brought it, he and the Rema did not bring it in the Shulchan Aruch, we cannot obligate people to endanger themselves in order to save others.