The supposed medicinal properties of precious stones are subjected to a searching criticism by the Veronese physician, Francesco India, writing in 1593.[235] After establishing the distinction between alimentary and medicinal substances, he proceeds to exclude from the latter category the jacinth, emerald, sapphire, etc., because although they could be reduced to a powder, they could not be dissolved, so that when taken in a potion they could be absorbed in the human system.[236] Hence no such effects could properly be ascribed to them as were to be expected from the regular and normal medicinal agencies. This writer ascribes the original use of such stones as remedies for malignant fevers and other dangerous diseases to the Arabs, adding that “had they not made this mistake and thus led many physicians into error, they would have been better worthy of praise.”[234] In fact he does not hesitate to pronounce the emphatic opinion that these stones are not remedial agents fit to be administered or used by any rational physician.[237] That powdered hematite (red oxide of iron) possesses an astringent quality and may really be looked upon as a medicine, he fully recognizes, more particularly its efficacy for the cure of diseases of the eye, but neither these nor similar qualities can be credited to sapphires, emeralds, or jacinths. At the same time he is not disposed to deny that these stones may have some subtle effect upon the body when worn, or when held in the mouth for a time. Thus he agrees with Avicenna (Ben Sina) that a jacinth worn over the heart may strengthen that organ, for he knows of the power inherent in jasper to check a hemorrhage. In a word his argument is principally directed against the internal use of powders made from these hard and unassimilable stones.[238] Robert Boyle, writing in 1663, attempts to show that the theory of the therapeutic action of precious stones is not incompatible with observed facts. In this connection he says:[239]