פירוש על נזיר 55:1

Rather, is it not referring to a lengthy naziriteship, and nevertheless it teaches: He starts counting immediately - from the day that he is presently, and he finishes that series of days that began before he was confirmed [a leper]. But the days in which he was confirmed [a leper] do not count for him.

What, is it not that Rabbi holds that they decreed impurity on it with regard to the air - and as for this case, since the air enters from above when they are open, or through openings, he would be impure, since he has entered the airspace of the land of the nations.

To a naziriteship of fifty days etc. [where he sat and observed twenty days and developed leprosy. He shaves on account of his leprosy and the days in which he was confirmed do not count for him] - because if you will say that they do count for him, he won't have enough [time remaining] in order to grow his hair after his leprosy-related shaving. Therefore following that he will need to sit for thirty days of naziriteship so that he has hair growth.

And Rabbi Yosei, son of Rabbi Yehuda, holds with regard to the earth - and not with regard to the air -- and since the floor of the chest, box or cabinet interposes between him and the earth, he would be deemed pure.