All spittle that is found in Jerusalem is [assumed to be] tahor, except for that [found] in the upper market; [these are] the words of R’ Meir.  R’ Yose says: At other times of the year, whatever [spittle] is in the middle [of the street] is [assumed to be] tamei, and whatever is on the sides is tahor. But at the time of the pilgrimage festival, whatever [spittle] is in the mid-dle [of the street] is [assumed to be] tahor, and whatever is at the sides is tamei, because, since they are a minority, they withdraw to the sides.