Levítico 21:12 Halajá: Sefer HaChinukh & Kitzur Shulchan Arukh

That the priests not go out from the Temple at the time of the service: That the priests not go out from the Temple at the time of the service, as it is stated (Leviticus 10:7), “And from the entrance of the Tent of Meeting you shall not go out, lest you die.” And this prevention was repeated likewise with the high priest, and it stated (Leviticus 21:12), “And from the sanctuary he shall not go out.” And the language of Sifra, Shemini, Mekhilta d'Miluim 42-43 is, “‘And from the entrance of the Tent of Meeting’ — it could be [that they shall not go out] at the time of the service and [also] not at the time of the service. [Hence] we learn to say, ‘And from the sanctuary he shall not go out and he will not profane’ — [...] it would be said, when he is officiating. [...] ‘For the anointing oil of the Lord is upon you’ — I only have Aharon and his sons who were anointed with the oil of anointment, if they went out while serving, they would be liable for death; from where [do I know] for all of the priests of the generations? As it is stated, ‘for the anointing oil of the Lord is upon you.’”

The Kohein is commanded not to defile himself through any form of contact with the deceased. Even an abortive fetus, whose limbs have not yet been connected with ligamentous tissue, is considered in this regard as a dead body. (If, however, the abortion occurred within forty days from conception, it is considered like water). The dead body need not be in its entirety, for this law applies even to things that have separated from the corpse such as blood and the like. He is also forbidden to defile himself through contact with the severed limb of a living person, if there is enough flesh on it that were it still connected, it would have possibly healed. Even if it is his own limb, he is forbidden to defile himself by touching it. A Kohein is forbidden to enter a house where a person is close to death, and even though a gosseis (dying person) is considered alive with regard to everything else, and he is not considered impure, nevertheless, the Kohein [by entering such a house] violates the command, "You shall not desecrate,"¹Leviticus 21:12. A Kohein is forbidden to attend Medical School. See Igros Moshe, Yorah Deiah III 155. for he is commanded to guard his priesthood so that it does not become profaned, and the gosseis may die at any moment.