Rambam - 1 Chapter a Day

I.e., even if the special laws that apply to a backbone, a skull, or a quarter of a kab of bones (see Chapter 2, Halachot 8-9) do not apply, one would contract impurity for touching or carrying any one bone that is more than a barley-com in size.

For the special laws that apply to a limb from a living person (Chapter 2, Halachah 3) apply only when that limb is intact.

I.e., the conditions applying to rekev, that the corpse have been buried naked, in a marble coffm, etc. (Chapter 3, Halachah 4), must apply to each one of them, nor may they have been buried together (Chapter 3, Halachah 5). If these specifications are met and then one takes a handful of rekev from one corpse and combines it with a handful of rekev from another corpse, the combined amount imparts ritual impurity (Kessef Mishneh).

And impart ritual impurity as they would have had they come from one corpse.

Since netzal is decomposed flesh and like flesh, an olive-sized portion imparts impurity, it can be combined with flesh to reach that measure.

But not when touched, for like rekev, a divided bone cannot be touched at once (Chapter 2, Halachah 11). See also the following halachah.

Similarly, it imparts impurity when carried, but not when touched. Rambam Le’Am opines that if in fact one does touch an entire portion of a bone the size of a barley com at one time, he becomes impure even if the bone is not intact.

Even though the entire measure is not considered intact, that is not significant with regard to these ways of contracting impurity.

One does not contract impurity by touching unless one touches an olive-sized portion of the flesh at the same time. Hence, in the present instance, if one touches only a portion of the flesh, it is not considered as if one touched the entire measure. For, as the Rambam proceeds to explain, the fact that there is an olive-sized portion of the flesh present and that appears as a single entity is not significant. In this instance as well, Rambam Le’Am opines that if in fact one does touch an entire olive-sized portion of the flesh at one time, he becomes impure even if the portion is not intact (see the gloss of Rabbi Akiva Eiger to Hilchot Sha’ar Avot HaTum’ah 1:12).

Provided it is still intact, as a single entity.

And thus becomes a single mass. The rationale is that it is being joined together due to man’s influence and a fusion brought about by man is not significant.

For example, an olive-sized portion of flesh. Even though it is divided, when brought into the house, the entire olive-sized portion is under that shelter. The Ra’avad adds that this law applies even if there is no shelter to cause the two entities to be considered as one. If one touches half an olive-sized portion of a corpse with one hand and half with the other hand, he becomes impure, because he is touching an entire olive-sized portion at the same time.

I.e., naturally, as a matter of course.

Even though only a portion of the bone has been brought into the house, it is considered as if the entire bone was brought in. This applies even if all of the flesh was outside the house, the bone is considered as a yad, “handle,” for the flesh and thus an extension of it. Thus bringing a portion of the bone into the house is considered as bringing the flesh in.

Unless a sufficient quantity of the impure substances were brought inside.

The minimum measure required to impart ritual impurity.

Because the entire quantity of two handfuls is under the same shelter. Hence it is considered as combined.

As the Rambam proceeds to explain, at the time the blood was brought in, the house and all of its contents contracted impurity. When the blood was absorbed, however, that impurity departed. Even if the entire quantity of blood was not absorbed, as long as less than a revi'it remains, the house does not contract impurity.

We assume that it was consumed or dragged out of the house by a cat, a weasel, or the like (Rav Yosef Corcus, as quoted by the Kessef Mishneh).

I.e., we assume that the piece of flesh found is the piece that was lost and not a new piece of flesh (ibid.).

Thus any article or any person who was in the house at any time during this period is retroactively considered as impure.

In the Rambam's Commentary to the Mishnah (Ohalot 3:3), he interprets this as referring to the open space within a structure. If the structure projected over it, it becomes impure. The Tosafot Yom Tov interprets the mishnah differently, explaining that it refers to open space outside a structure. If it collects in one place and a person stands over it, he becomes impure. There are some who maintain that the Rambam changed his mind and accepted that interpretation here.

For when liquids are flowing on an incline, they are not considered as connected. Note a parallel in Hilchot Tum’at Ochalin 7:6.

Even though the lintel of the house covered the doorstep, it is not considered as if the blood was under the house, because the blood did not come to rest there (ibid.).
The Ra’avad explains that the rationale is that the blood is not considered as a single entity, because it became separate when it flowed because of the incline. He maintains that this law applies only to blood. It must be a single mass, for it is written (Deuteronomy 12:23): “The blood is the soul.” And blood can only be a medium for the soul when it is connected as a single entity. This does not apply to flesh or bones. Even if they are not intact, their mass is calculated together.

This applies even if a portion of the revi’it of blood was not under the lintel. As long as it is intact as a single unit, it brings about impurity (Kessef Mishneh in the name of Rabbenu Asher).

In which instance, the garment is impure, but it does not impart impurity to others.

To see whether or not a revi’it is discharged.

As mentioned in Chapter 1, Halachah 11, impurity may be conveyed through ohel in three ways: one enters a shelter where a corpse is located, one stands over a corpse, or the corpse is held over the person’s body. As the Rambam proceeds to explain, since all of the ways of contracting impurity come from the same category, they may be combined.

We are speaking about an instance where the portion of the person’s body touching the corpse was not under the same shelter as the portion to which the concept of ohel applied [the Rambam’s Commentary to the Mishnah (Ohalot 3:1)].

This refers to an instance where the person carried the portion of the corpse without touching it.

E. g., carrying and touching a portion of a carcass of a dead animal (ibid.).