The Hindoos, whose books on the healing art date back to 1500 B.C., regarded sickness as the result of the operation of malevolent deities who were either to be propitiated by prayers, offerings, charms, and sacrifices, or to be overcome with the aid of friendly gods. The early Greeks when suffering from disease were cured, not by means of medicine, but by religious observances, and particularly by the "temple-sleep," in which they dreamt dreams which the priests interpreted, and in which were found the suggestions for remedy. It was Hippocrates, in 460 B.C., who first proclaimed that disease was not of supernatural origin, and that it could not be combated or cured by magic. But for many centuries later in Europe the Black Art had greater sway than rational treatment. In Sweden it is even now common for the lower classes to ascribe sickness to the visitation of spirits (Nisse), who must be mollified by pouring liquor into a goblet and mixing with it the filings of a bride-ring, or filings of silver, or of any metal that has been inherited. The mixture is taken to the place where the man is supposed to have caught his illness, and is poured over the left shoulder, not a syllable being uttered the while. After the performance of this ceremony the invalid may hope to recover. Consecrated grave-mould is supposed by many primitive races to have particular properties as a medicine. The Shetlander who has a "stitch in his side," cures himself by applying to the affected part, some dry mould brought from a grave, and heated, care being taken to remove the mould and to return it before the setting of the sun. In the neighbouring isles of Orkney, magic is also resorted to as a remedy for disease. Perhaps the least harmful of the rites is the washing of a cat in the water which had previously served for an invalid's ablutions, the confident belief being that the disease would by this means be transferred to the animal. This custom of "substitution" is found in many races, and is one of the most interesting subjects introduced to the student of folk-lore.