Eiruvin, Chapter 1, Mishnah 7. This mishnah deals with the question of what materials may be used to make a lechi, and in particular whether a lechi may be made from a living creature. From this discussion the mishnah broadens the question to other areas of halachah: do other laws and categories require an inanimate object, one with no life in it, or can they be fulfilled even with something alive?
"Bakol osin lechayayin":
The mishnah rules: "Bakol osin lechayayin, afilu b'davar sheyesh bo ruach chaim" - a lechi may be made from anything at all, even from a living creature. One ties it to the wall, and from that point on it is permitted to carry in the alleyway on Shabbos. We are not concerned about two possible problems:
That the living creature will run off from its place - since it is tied down.
That it will lower itself to the ground, so that it will no longer stand ten tefachim high as required.
If the lechi was set up properly, there is no need to be concerned about these possibilities.
"Rabbi Yosei oser" - in his opinion one may not make a lechi from an animal, out of concern that the animal will die and shrivel up, leaving it without the required height, and people will not notice the change or pay attention to it. The first tanna, however, is not concerned about this, since death is not such a common occurrence.
The Law of a Golel:
The mishnah now extends a similar dispute to another area - the law of the golel. The Rishonim offer various explanations of what exactly the golel is, but in any case it is something connected to the burial of the deceased:
Some understand that the golel is the stone placed on top of the grave, alongside which there is a dofek - the item that supports the golel.
Others understand that the golel is the cover of the coffin itself.
By way of introduction, the Torah includes the golel among the items that contract tumah, even though it is not in direct contact with the body of the deceased. According to many opinions, even after it ceases to serve as a golel that same tumah remains upon it, and this tumah is a seven day tumah, like anything that comes into contact with a dead body.
The mishnah states "u'metamei mishum golel" - a living creature placed as the covering of the grave or the coffin, even temporarily, conveys tumah as a golel. "Rabbi Meir metaher" - in his opinion an animal cannot serve as a golel, it does not contract the tumah associated with a golel, and it does not acquire this halachic status.
Writing a Get on Something Alive:
The mishnah moves on to yet another area of halachah: "V'kosvin alav gittei nashim" - a man may write a get for his wife on the body of a living creature, for example on the horn of a cow, and then give her the cow. He may not cut off the horn, because in the laws of gittin there may be no significant interruption between the writing and the giving, such as cutting off the horn; therefore he must give the woman the entire cow and not the horn alone. In any event, the mishnah teaches that a living creature may serve as the surface on which a get is written.
"Rabbi Yosei HaGlili posel" - this is not the Rabbi Yosei mentioned earlier, but rather Rabbi Yosei HaGlili, who holds that one may not use a living creature, and he derives this from the verse that describes the get as a "sefer kerisus": just as a sefer is something with no life in it, so too only lifeless items are valid for a get, and not living ones.
In summary: in this mishnah we learned that according to the first tanna a lechi may be made from anything at all, even from an animal, and we are not concerned that it will run away or lower itself, while Rabbi Yosei forbids it out of concern that it will die and shrivel up. They also disagree about the extensions of this principle: a living creature serving as the covering of a grave conveys tumah as a golel, while Rabbi Meir rules that it does not; and a get may be written on the body of an animal, while Rabbi Yosei HaGlili invalidates it based on the derivation from "sefer kerisus".