When ye be come into the land of Canaan, which I give to you for a possession, and I put the plague of leprosy in a house of the land of your possession;
Leprosy in a house. This law was prospective, not being to come into operation until the settlement of the Israelites in Canaan. The words, "I put the leprosy," has led many to think that this plague was a judicial infliction from heaven for the sins of the owner; while others do not regard it in this light, it being common in Scripture to represent God as doing that which He only permits in His providence to be done. Assuming it to have been a natural disease, a new difficulty arises as to whether we are to consider that the house had become infected by the contagion of leprous occupiers; or that the leprosy was in the house itself. It is evident that the latter was the true state of the case from the furniture being removed out of it on the first suspicion of disease on the walls.
Some have supposed that the name of leprosy was analogically applied to it by the Hebrews, as we speak of cancer in trees when they exhibit corrosive effects similar to what the disease so named produces on the human body; while others have pronounced it a mural efflorescence, or species of mildew on the wall, apt to be produced in very damp situations, and which was followed by effects so injurious to health, as well as to the stability of a house, particularly in warm countries, as to demand the attention of a legislator.
'The reddish patches may have been caused by species of fungus, called dry-rot (merulius lacrymans), which appears at first in the floors and beams of buildings, in the form of white cottony patches, from one to eight inches broad, afterwards developing over their whole surface a number of orange or reddish-brown irregular folds, distilling drops of moisture when perfect;-hence, the specific name. This insidious disease, once established, spreads with amazing rapidity, destroying the most solid house in a few years. So virulent is its nature, that it extends from the woodwork of a house even to the walls themselves, and by penetrating their interstices, crumbles them to pieces. The houses of Palestine, numbers of which were built of mud or wood, were peculiarly exposed to its ravages; and when once this fungus obtained a footing, the desperate remedy proposed by Moses had often to be resorted to after the failure of every attempt to extirpate it' ('British and Foreign Evangelical Review,' No. 47:, article 'Biblical Botany,' by H. Macmillan).
Moses enjoined the priests to follow the same course, and during the same period of time, for ascertaining the true character of this disease as in human leprosy-in case of being found leprous, to remove the infected parts, or if afterwards there appeared a risk of the contagion spreading, to destroy the house altogether; and remove the materials to a distance. The patches were frequently green, especially on the walls of houses reared of stone. The stones were probably rough, unhewn stones, built up without cement, in the manner now frequently used in fences, and plastered over, or else laid in mortar. The oldest examples of architecture are of this character. The very same thing has to be done still with houses infected with mural salt. The stones covered with the nitrous encrustation must be removed; and if the infected wall is suffered to remain, it must be plastered all over anew.