When ye be come into the land of Canaan, &c.— After having spoken of the leprosy of persons and of garments, the sacred writer proceeds to that of houses, concerning which we have already said something in the first note on the last chapter, especially with respect to the opinion derived from the words, I put the plague into a house, &c. that this was a punishment inflicted by the hand of God. "Though it is more difficult to account for the infection of houses," says Dr. Mead, "yet, upon a serious consideration of the different substances employed in building the walls of houses, such as stones, lime, bituminous earth, hair of animals, and other such things mixed together, it appears probable to me, that they may, by a kind of fermentation, produce those hollow, greenish or reddish strakes, in sight lower than the wall, or within the surface, (Leviticus 14:37.) which, as they in some measure resembled the leprosy on the human body, were named the leprosy in an house; for bodies of different natures very easily effervesce upon being blended together: wherefore we may reasonably suppose that this moisture or mouldiness, gradually coming forth and spreading on the walls, might prove very prejudicial to the inhabitants by its unwholesome smell, even without having recourse to any contagious quality in it. Something analogous to this is frequently observable in our own houses; where, when the walls are plaistered with bad mortar, the calcarious and nitrous salts sweat out upon their surface, of a colour almost as white as snow." Calmet solves this extraordinary phaenomenon upon the same principles with those mentioned before; observing, that "a particular sort of vermin was bred in the mortar and stones of the infected houses. This was one of the tokens of a house being infected. There were some others besides, which were a kind of rust or scurf, that spread itself along the walls.
In all these cases, the priests were directed to shut the house up for a week: and it is probable, they made some kind of fumigation during that time, though no mention is made of it; else we cannot see how the bare shutting it up could contribute to the cure. If, upon the opening it again, they found the marks gone, they pronounced it clean; if not, they caused them to be scraped off every where, and the house to be shut up another seven days: but if that did not work the cure, they ordered it to be demolished, and such materials of it only to be preserved as were free from the infection, in order to build it up in some other place." See Calmet's Dissert. and the Univ. Hist. vol. 3: The Jewish writers, however, judge very differently of this matter, and consider this plague as a supernatural punishment for calumny and detraction in particular; an opinion, which seems to have arisen from the case of Miriam: and they tell us, that it first infected the walls of the house, and, the offender repenting, went no further; but, if he persisted, it proceeded to his household stuff; and, if he still went on, invaded his garments, and at last his body. This opinion may, perhaps, gain some confirmation from the remarks of a physician in the southern parts of France, that the leprosy, though hereditary, never goes beyond the third, or, at the most, the fourth generation; an observation, says Michaelis, which I use to explain the 5th verse of the 20th chapter of Exodus.