Treatise in the Mishnah and the Tosefta dealing with defilement through a dead human body, through the dead body of an animal, or through contact with one that is diseased; based on Num. xix. 14-16. In the Tosefta it is called Ahilot ("Tentings"), which name occurs also in the Palestinian Talmud (M. Ḳ. ii. 81b). Ohalot is the second tractate in the mishnaic order of Seder Ṭohorot and is divided into 18 chapters and 133 paragraphs.
- Ch. i.: The various kinds of defilement by a dead human body (§§ 1-3); the degrees of defilement sustained by an individual and the degrees of defilement sustained by a vessel (§ 4); the defilement of person or clothing through contact with one having a discharge (§ 5); defilement by touching the dead body of either man or beast does not occur until after formal verification of death (§ 6); contact with a single member, provided it is entire, defiles, even though it is less than normal size (§ 7); enumeration of the 248 parts of the human body (§ 8).
- Ch. ii.: The amount of flesh, bones, or blood, of ashes of an incinerated body, or of dust from a grave, which is capable of defiling (§§ 1-2); those parts of a corpse which defile through being touched or carried, but not by their presence in the tent; other things which defile by being merely touched or carried (§ 3); the cover of a tomb and its walls defile by being touched, but not by being carried (§ 4); cases in which the given quantity of flesh, blood, or bones is diminished or is divided, or in which the given quantity is from two or more bodies (§§ 5-7).
- Ch. iii.: Various defilements comprised under the same name (§ 1); blood which has been spilled upon, or has soaked into, a garment (§ 2); cases in which the teeth, hair, or nails of a corpse defile (§§ 3-4); blood that defiles and blood that does not defile (§ 5); how large openings, as doors and windows, must be, on the one hand, to enable defilement to spread, or, on the other hand, by allowing uncleanness to escape, to protect other exits against defilement (§§ 6-7).
- Ch. iv.: In regard to a tower, and the relation between a cabinet standing in the house or in the door-way and the house itself, in connection with uncleanness in either.
- Ch. v.: The fireplace within and the chimney without the house. (§ 1); things in a dormer-window, between the house and the roof, protect the roof from uncleanness in the house (§§ 2-5); cases in which the covering of a well or cistern gives protection against defilement (§§ 6-7).
- Ch. vi.: How men and vessels may be regarded as tents in so far as they defile, but do not protect against defilement (§§ 1-2); the relation of the house or the roof to the outer wall, the partition wall, and the floor, in respect to any uncleanness in them (§§ 3-7).
- Ch. vii.: Uncleanness which penetrates vertically in both directions; the slanting roof and the slanting sides of a tent (§§ 1-2); the doors of a house in which there is a corpse (§ 3); defilement in connection with a still-born child (§§ 4-5); when the unborn child may be cut up while in the womb and removed piecemeal in order to save the life of the mother and when the child may not be injured in spite of the danger to the mother (§ 6).
- Ch. viii.: Things which, being regarded as "tentings," may defile other things, but which may, on the other hand, protect from uncleanness (§§ 1-2); things which defile but which can not protect from defilement (§ 3); things which protect from defilement and which can not defile (§ 4); things which neither protect from nor cause defilement (§ 5).
- Ch. ix.: The relation between a house and a basket in it (§§ 1-10); a basket or barrel in the open air, and circumstances in which uncleanness in it spreads upward or downward; defilement in connection with a tomb hewn in the rock (§§ 11-16).
- Ch. x.: Openings in a house with reference to uncleanness in the house or above the openings.
- Ch. xi.: The case of a fissure in the roof of a house or in a vestibule (§§ 1-2); the case of one who, leaning out of a window, places a covering over a corpse (§ 4); the case of those who, while bearing a body to burial, step over a person lying in the doorway (§ 5); concerning a dog which has eaten of the flesh of a corpse (§ 7); other details in regard to the covering of a cistern (§§ 8-9).
- Ch. xii.: Further details in regard to circumstances under which defilement spreads, or does not spread, upward or downward.
- Ch. xiii.: The size of windows or other openings with respect to the entrance or the removal of uncleanness (§§ 1-4); things in an opening which render it "smaller" and things which do not render it "smaller" (§§ 5-6).
- Ch. xiv.: The connection of moldings with uncleanness.
- Ch. xv.: Boards lying side by side or above one another with reference to uncleanness (§§ 1-3); uncleanness in a divided house, or in one filled with straw, grain, etc. (§§ 4-7); the entrance to a tomb, and the things in connection with it which may defile (§§ 8-9).
- Ch. xvi.: How far movable things, as tents, may spread uncleanness (§§ 1-2); when a place in which one or more bodies have been buried must be recognized as a burial-place; how a field in which a grave has been found may be purified (§§ 3-5).
- Ch. xvii.: When a field in which a grave has been plowed through becomes a burial-place ("bet ha-paras").
- Ch. xviii.: Further details regarding the three kinds of "bet ha-paras," and how they may be purified (§§ 1-6); fields on the frontier between Palestine and Syria; houses and dwellings of the Gentiles, and under what circumstances they are unclean (§§ 7-10).
The Tosefta to this treatise, also divided into eighteen chapters, contains various details which serve to explain the Mishnah. For instance, Tosefta v. 11-12 explains in detail why the Bet Hillel, as Mishnah v. 4 says, revoked its original decision, and how the Bet Shammai decided. Similarly Tosefta xviii. 13 explains what is meant by "the eastern side of Cæsarea" ("mizraḥ Kisrin" Mishnah xviii. 9). Among the sayings of R. Joshua given in the Tosefta are the following: "Whoever learns without taking pains is like him who sows without reaping,for his studies will profit him nothing." "Whoever learns the Torah and straightway forgets it, is like unto a woman who gives birth to children who die immediately after birth" (Tosef. xvi. 8).