Before the time of Moses leprosy was well known. The first mention made of it in Holy Writ is in the fourth chapter of Exodus. God, having chosen Moses to deliver the Hebrews from the tyranny of the Egyptians, orders him to present himself before his afflicted people and to announce himself to them as their deliverer. Moses objected, saying: “They will not believe me, nor hearken unto my voice; for they will say, The Lord hath not appeared unto thee!” Then the Lord, to convince Moses of his divine mission, said unto him, “Put now thine hand into thy bosom,” and he put his hand into his bosom; and when he took it out, behold his hand full of leprosy, white as snow—“_instar nevis_.” Here, then, was leprosy easy to recognize, since it had the whiteness of snow. Let us not forget this peculiar feature, for we shall see it again later. From this incident we see clearly that the disease was by no means unknown to Moses, because on seeing his hand he said: “_Leprosam instar nevis._” Therefore we have a right to believe that the disease existed before Moses. To the support of this opinion Dom Calmet, in his _Biblical Dictionary_, cites Manetho the Egyptian, Lysimarchus, Appian, Tacitus, and Justin, who have advanced the idea that the Jews went out from Egypt on account of the leprosy. Each one of these historians narrates the events in his own fashion, but all agree that the Hebrews who left Egypt were attacked by leprosy. Not only does leprosy fasten on mankind, but it clings to clothing and to the stone walls of houses. It is to be presumed, however, that the leprosy brought by the Israelites out of Egypt was not of this malignant type; for Moses, by the order of God, takes pains to mention another and more virulent kind known in the land of Chanaan, the promised land of the Israelites. In Leviticus, chapter xiii., we find the following: “If there be a spot, greenish or reddish, in the garment, of wool or of skin, the garment must be shown to the priest; and the priest shall look on the plague, and shut it up for seven days; and if at the end of the time the spots have spread, the priest will burn the garment, for it is a fretting leprosy. If the priest find, however, that the spots have not spread, he shall order the garment to be washed; and, behold, if the plague have not changed his color, and be not spread, it is unclean: thou shalt burn it in the fire.”