Leviticus 13:12,13

And if a leprosy break out abroad in the skin, &c.— It may appear extraordinary, that a man, who is all over leprous, should be pronounced clean, and yet one, who is but partially leprous, should be unclean. "The difficulty contained in this passage will vanish," says Dr. Mead, "if we suppose, as it manifestly appears to me, that it points out two different species of the disease: the one, in which the eroded skin was ulcerated; the other, which spread on the surface of the skin only, in the form of rough scales; and from this difference it happened that the former species was, and the other was not, contagious." See his Epist. Medicinal. lib. 7: Ephesians 2.