If a zav and a ritually pure person climbed a tree that has little strength, which shook as they climbed it, or if they climbed onto a branch that has little strength, the ritually pure person is rendered ritually impure. One of the ways a zav imparts impurity is by movement, and here the zav is viewed as having moved the pure person.

The Gemara asks: What are the circumstances of this tree that has little strength, i.e., how is a tree with little strength defined? The Sages of the school of Rabbi Yannai say: It is any tree whose trunk is not broad enough that one can hollow out a vessel of a quarter-kav from it. What are the circumstances of a branch that has little strength? Reish Lakish said: It is any branch concerning which its circumference can be hidden, i.e., inserted, in a person’s fist. A branch of this size is generally not strong enough to hold two people without shaking.

We learned in a mishna elsewhere (Oholot 18:6): With regard to one who walks in an area in which uncertainty exists concerning the location of a grave or corpse [beit haperas], if he treads over stones that he can move as he walks, raising concerns that he might have moved a bone of a corpse and thereby rendered himself impure, or if he was in that location, on the back of a person or riding on an animal that had little strength, he is impure, as he is considered to have moved the impurity himself.

The Gemara asks: What are the circumstances of a person that has little strength? Reish Lakish said: Any person whose knees knock against each other when someone rides upon him. What are the circumstances of an animal that has little strength? The Sages of the school of Rabbi Yannai say: Any animal that releases excrement due to strain when a person rides upon it.

§ As the Gemara has cited the rulings of the school of Rabbi Yannai with regard to measurements, it now cites similar halakhot that the Sages of the school of Rabbi Yannai state: With regard to prayer and with regard to phylacteries, the measure is four kav.

The Gemara inquires: What is the relevance of this measure with regard to prayer? This is as it is taught in a baraita: With regard to one who carries a load on his shoulder and the time for prayer arrives, if the load is less than four kav, he lowers it behind him while still holding it and prays, as a light load of this size does not interfere with prayer. If the load is four kav, he places it on the ground and prays.

What is the relevance of this amount with regard to phylacteries? This is as it is taught in a baraita: If a man was carrying a load on his head and he had phylacteries on his head, if the phylacteries were being crushed under the load it is forbidden to leave them on his head, but if they were not being crushed, it is permitted. With regard to which load did the Sages state this halakha? They stated it with regard to a load of four kav.

Rabbi Ḥiyya teaches: With regard to one who removes garbage by carrying it on his head and has phylacteries on his head, he may not move the phylacteries to the side to prevent them from being crushed, and likewise he may not tie the phylacteries of the head to his loins because he thereby treats them in a manner of degradation. But he may tie them on his arm in the location where the phylacteries of the hand are placed.

The Sages said in the name of the school of Sheila: It is forbidden to place on the head of one that has phylacteries on it even the scarf in which they are wrapped. The Gemara asks: And how much does Rabbi Sheila permit one to place on his head while wearing phylacteries? Abaye said: Even as little as one-quarter of one-quarter of the smallest measurement of Pumbedita is still forbidden from being placed on one’s head.

§ The mishna teaches: Rabbi Yehuda says: What fixed measure is a pile? Rather, the relevant issue is whether it has a crop equivalent to the measure of seeds for dropping in a field in order to sow it. The Gemara asks: And how much is equivalent to the measure of seeds for dropping in a field in order to sow it? Rabbi Ami says that Rabbi Yoḥanan says: Four se’a for the amount of land sufficient to grow a kor. Rabbi Ami himself, though, says eight se’a for the amount of land sufficient to grow a kor. A certain elder said to Rav Ḥama, son of Rabba bar Avuh: I will explain it to you: In the years of Rabbi Yoḥanan the land was fat, while in the years of Rabbi Ami the land was lean, and it was therefore necessary to double the amount of seed for each unit of land.

We learned in a mishna elsewhere (Pe’a 5:1): If the wind scattered the standing sheaves so that it is no longer known which gleanings fell from the sheaves during the harvest and belong to the poor, one evaluates how many gleanings it was fit to produce, and he gives these to the poor. Rabban Shimon ben Gamliel says: He gives to the poor the amount equivalent to the measure of seeds dropping in the course of harvesting.

The Gemara asks: And how much is the amount equivalent to the measure of seeds dropping in the course of harvesting? When Rav Dimi came from Eretz Yisrael he said that Rabbi Elazar said, and some say it was Rabbi Yoḥanan: Four kav for a kor. Rabbi Yirmeya raised a dilemma: Does this mean for a field that requires a kor of seed to plant it, or for a kor of produce? And if it is the former, does it refer to sowing by hand or to sowing by oxen?

The Gemara answers: Come and hear, as when Ravin came from Eretz Yisrael he said that Rabbi Avuh said that Rabbi Elazar said, and some say that Rabbi Yoḥanan said: Four kav for a field sown with a kor of seed. The Gemara comments: And the other question should still raise a dilemma for you: Does this refer to sowing by hand or to sowing by oxen? No answer was found for this question, and the dilemma shall stand unresolved.

MISHNA: In the case of one who receives a field from another to cultivate and grasshoppers consumed it or it was wind blasted, if it is a regional disaster which affected all the fields in the area, the cultivator subtracts from the produce he owes as part of his tenancy. If it is not a regional disaster, the cultivator does not subtract from the produce he owes as part of his tenancy. Rabbi Yehuda says: If the cultivator received it from the owner for a fixed sum of money, whether this way, i.e., there is a regional disaster, or whether that way, i.e., there was no regional disaster, he does not subtract the produce he owes as part of his tenancy.

GEMARA: The Gemara asks: What are the circumstances of a regional disaster? Rav Yehuda said: If, for example, most of that valley in which the field was located was wind blasted, it is considered a regional disaster. Ulla said: If, for example, four fields were wind blasted on its four sides, it is considered a regional disaster.

Ulla also said: They raise the following dilemma in the West, Eretz Yisrael: If one furrow was wind blasted along its entire length, adjacent to other fields that were wind blasted, what is the halakha? Is this considered to be part of the regional disaster? Conversely, if one furrow remained undamaged along its entire length, what is the halakha? Does the remaining furrow mean that the entire field is not considered to be part of the regional disaster? If a fallow field divided between the cultivated fields and the fields that were wind blasted, what is the halakha? Alternatively, if there was a field of fodder between this field and the others that were wind blasted,