The Gemara raises an objection: There is a unique halakha with regard to the impurity of a zav and a menstruating woman: In a case where one of them sits on an item, including one that cannot become ritually impure, e.g., a stone, and beneath that item is a vessel, that vessel becomes impure, even if their weight has no effect on the vessel, as in the case of a very heavy stone. If the verse compares the status of the menstrual blood to the status of the menstruating woman, as derived above, one can infer as follows: Just as a menstruating woman transmits impurity to items that lie beneath a very heavy stone, so too, her menstrual flow also transmits impurity to items that lie beneath a very heavy stone.

Rav Ashi said in response: Items designated for lying or sitting also transmit impurity to items that lie beneath a very heavy stone. The verse states with regard to an item of this kind, which was rendered impure by a zav: “And whoever touches anything that was under him shall be impure until the evening, and he that carries them shall wash his clothes, and bathe himself in water, and he shall be impure until the evening” (Leviticus 15:10). The term “them” is an exclusion, indicating that items designated for lying or sitting transmit impurity to items that lie beneath a very heavy stone, but menstrual blood does not.

§ The mishna teaches: And the flesh of a corpse transmits impurity both when moist and when dry. The Gemara asks: From where do we derive this halakha? Reish Lakish said that this is as the verse states: “Or whoever touches any creeping thing by which he may be made impure, or a man from whom he may be made impure, from any impurity that he has” (Leviticus 22:5). The term “from any” is an amplification, indicating that one may become impure from any impurities that come from a dead person, whether they are moist or dry.

Rabbi Yoḥanan said that this halakha is derived from the verse: “And whoever touches in the open field one who is slain with a sword, or one who died, or the bone of a man, or a grave, shall be impure seven days” (Numbers 19:16). The verse indicates that the impurity of a dead man is similar to the impurity of a bone: Just as a bone is dry, so too here, with regard to the impurity of a corpse, it transmits impurity even when it is dry.

The Gemara asks: What is the practical difference between the inferences of Reish Lakish and Rabbi Yoḥanan? The Gemara answers that the practical difference between them is the case of a corpse which is so dry that it crumbles. Reish Lakish maintains it is impure, as the term “from any” indicates that a corpse transmits impurity in any form, whereas Rabbi Yoḥanan maintains it is ritually pure, as it is unlike a bone, which does not crumble.

The Gemara raises an objection to the opinion of Reish Lakish from a baraita: The flesh of a corpse that crumbled is ritually pure. The Gemara answers that this is not difficult, as the baraita there is referring to where the flesh is so dry that it has become like flour and is therefore classified as dust.

The Gemara raises an objection to the opinions of both Reish Lakish and Rabbi Yoḥanan from a mishna (Oholot 3:3): Everything that is in a corpse transmits impurity, except for the teeth, and the hair, and the nails. This is the halakha only when these items are separated from the body, but when they are attached to the corpse they are all impure. According to Rabbi Yoḥanan teeth should transmit impurity because they are similar to bones, while according to Reish Lakish they should be included in the term “from any.”

Rav Adda bar Ahava said: Only items that are similar to a bone transmit impurity: Just as a bone is an item that was created with him at the time of birth, so too, all items that transmit impurity are those that were created with him, whereas teeth are not present at the time of birth. The Gemara asks: But are there not the cases of hair and nails, which were created with him, and yet the mishna states that they are ritually pure?

Rather, Rav Adda bar Ahava said a different explanation: Only those items that are similar to a bone transmit impurity: Just as a bone is an item that was created with him and its root does not renew itself, i.e., if a bone is removed a new bone does not grow in its place, so too, any item that was created with him and whose root does not renew itself transmits impurity. The teeth were excluded from this category, as they were not created with him. The hair and nails were excluded, as even though they were created with him their roots renew themselves, since they grow again after they are cut off.

The Gemara objects: But isn’t there the case of skin, whose root renews itself, and this is as we learned in a mishna (Ḥullin 54a): In the case of an animal whose hide was removed [hageluda], Rabbi Meir deems it kosher, as the skin renews itself, and the Rabbis deem it an animal with a wound that will cause it to die within twelve months [tereifa] and unfit for consumption. The Gemara explains: And even the Rabbis deem it unfit only due to the fact that in the meantime, between the removal of the old hide and the growth of the new one, the air affects it and as a result it will die, but they concede that actually the skin’s root renews itself. And nevertheless we learned in a mishna (Ḥullin 122a): These are the entities whose skin has the same halakhic status as their flesh: The skin of a dead person, and the skin of a domesticated pig…and the skin of the hump of a young camel, etc.

The Gemara explains that it was stated with regard to that mishna that Ulla said: By Torah law, the skin of a dead person is ritually pure. And what is the reason the Sages said that it is impure? It is a rabbinic decree lest a person should fashion rugs for a donkey out of the skins of his deceased father and mother.

And some say a different version of the above discussion: Isn’t there the case of skin, whose root does not renew itself, and this is as we learned in a mishna (Ḥullin 54a): In the case of an animal whose hide was removed, Rabbi Meir deems it kosher, and the Rabbis deem it a tereifa and unfit for consumption, as its skin does not regrow? The Gemara explains: And even Rabbi Meir deems it fit only because the flesh cools and the animal heals, but he concedes that actually the skin’s root does not renew itself. Accordingly, the skin of a corpse should be impure. But Ulla said: By Torah law, the skin of a dead person is ritually pure.

The Gemara answers that when the opinion of Ulla was stated, it was stated with regard to the latter clause of that mishna: And for all of these skins, in a case where one tanned them or where one spread them on the ground and trod on them for the same amount of time it takes for tanning, they are no longer classified as flesh and are ritually pure, except for the skin of a dead person, which maintains the status of flesh. And with regard to this Ulla said that by Torah law the skin of a dead person, when one tanned it, is ritually pure. And what is the reason the Sages said it is impure? It is a rabbinic decree lest a person should fashion rugs out of the skin of his deceased father and mother.

The Gemara asks: But isn’t there the case of flesh, whose root renews itself, as when one’s flesh is cut it regrows and heals, and yet it is impure? Mar bar Rav Ashi says: Flesh does not renew itself, as although when someone is cut his flesh regrows and heals, a scar is formed in its place.

§ The mishna teaches: But ziva transmits impurity when moist, although not when dry. The Gemara asks: From where do we derive that ziva transmits impurity? As it is taught in a baraita that discusses the verse: “When any man has an issue out of his flesh, his issue, it is impure” (Leviticus 15:2). This taught with regard to ziva that it is impure.

The baraita asks: Why is this derivation necessary? Could this not be derived through an a fortiori inference? Since ziva causes impurity to others, i.e., to the one who emitted the discharge, is it not all the more so that ziva itself is impure? The baraita replies that the case of the scapegoat brought on Yom Kippur may prove that this inference is not valid, as it causes impurity to others, i.e., the dispatcher of the scapegoat is rendered impure, and yet the goat itself is pure. So too, you should not be surprised about this, the discharge of ziva, that even though it causes impurity to others, ziva itself is pure. Therefore, the verse states: “His issue, it is impure.” This taught with regard to ziva that it is impure.

The Gemara objects: But one may say that this statement, that the discharge of ziva transmits impurity, applies only to transmitting impurity by contact. But with regard to transmitting impurity by carrying it does not transmit impurity, just as it is with regard to the carcass of a creeping animal, which transmits impurity by contact but not by carrying. Rav Beivai bar Abaye said: A verse was not necessary to teach that ziva transmits ritual impurity by contact, as the halakha with regard to ziva is no less stringent than with regard to semen, which transmits impurity by contact.