The physicians of the age of Charles II. were wont to give their patients "mummy powder," that is, pulverised mummy. They argued that the mummy had lasted for a very long time, and that the patients ought to do so likewise. Pliny imagined that diamonds must be found in company with gold, because these are the most perfect substances in the world, and like should draw to like. Aurum potabile, or drinkable gold, was a favourite medical nostrum of the Middle Ages, because gold, being perfect, should produce perfect health. Among savages the belief that like is caused by like is exemplified in very many practices. The New Caledonians, when they wish their yam plots to be fertile, bury in them with mystic ceremonies certain stones which are naturally shaped like yams. The Melanesians have reduced this kind of magic to a system. Among them certain stones have a magical efficacy, which is determined in each case by the shape of the stone. "A stone in the shape of a pig, of a bread-fruit, of a yam, was a most valuable find. No garden was planted without the stones which were to increase the crop."(1) Stones with a rude resemblance to beasts bring the Zuni luck in the chase. (1) Rev. R. H. Codrington, Journ. Anth. Inst., February, 1881. The spiritual theory in some places is mixed up with the "like to like" theory, and the magical stones are found where the spirits have been heard twittering and whistling. "A large stone lying with a number of small ones under it, like a sow among her sucklings, was good for a childless woman."(1) It is the savage belief that stones reproduce their species, a belief consonant with the general theory of universal animation and personality. The ancient belief that diamonds gendered diamonds is a survival from these ideas. "A stone with little disks upon it was good to bring in money; any fanciful interpretation of a mark was enough to give a character to the stone and its associated Vui" or spirit in Melanesia. In Scotland, stones shaped like various parts of the human body are expected to cure the diseases with which these members may be afflicted. "These stones were called by the names of the limbs which they represented, as 'eye-stone,' 'head-stone'." The patient washed the affected part of the body, and rubbed it well with the stone corresponding.(2) (1) Codrington, Journ. Anth. Soc., x. iii. 276. (2) Gregor, Folk-Lore of North-East Counties, p. 40.