There are [items] that spread tumah and act as barriers [against tumah], [items that] spread tumah but do not act as barriers [against tumah], [items that] act as barriers [against tumah] but do not spread [tumah], and [items that] do not spread [tumah] and do not act as barriers [against tumah]. These spread [tumah] and act as barriers [against tumah]: a chest, a box, a cabinet, a large straw basket, a large reed basket, and the water tank of an Alexan-drian ship — if they have [flat] bottoms and can contain forty se’ah of liquid, which is two kors of dry measure; a curtain, a work apron, a bed cover, a sheet, matting, and a mat, if they have been made into a tent; a herd of animals, whether nonkosher or kosher; lairs of wild animals and nests of birds, a bird that is resting, and one who makes a place for her son among the stalks; the iris, the kissom, chamor greens, the Greek gourd, and food that remains tahor. R’ Yochanan ben Nuri disagrees concerning food that remains tahor, except for a pressed cake of figs.