Eruvin 4: The Seven Species and What They Teach

More on the phrasing of tefachim and amot: they're happy and sad! Also: All those measurements are "halakhah le-Moshe mi-Sinai." Or are they from the Torah itself? Or are the Torah sources an asmakhta? The verse of the seven species has implicit in it the measurements that each of those species represents, from the amount of time before which a house of tzaraat would render a visitor's clothes impure... to the smallest amount of food that is prohibited on Yom Kippur. Are the seven species convenient, as the produce of the Land of Israel, or are they some kind of prototype for the measurements? Plus: chatzitzah - barriers in the mikveh, and the potential subjectivity of what defines something as a barrier.