The first writer to intimate the similarity in structural material or substance between pearls and the interior of the shell in which they are formed, appears to have been Anselmus de Boot (_circa_ 1600), who wrote that the pearls “are generated in the body of the creature of the same humour of which the shell is formed; ... for whenever the little creature is ill and hath not strength enough to belch up or expel this humour which sticketh in the body, it becometh the rudiments of the pearl; to which new humour, being added and assimilated into the same nature, begets a new skin, the continued addition of which generates a pearl.”[50] The Portuguese traveler, Pedro Teixeira (1608), stated: “I hold it for certain that pearls are born of and formed of the very matter of the shell and of nothing else. This is supported by the great resemblance of the pearl and the oyster-shell in substance and color. Further, whatever oyster contains pearls has the flesh unsound and almost rotten in the parts where the pearls are produced, and those oysters that have no pearls are sound and clean fleshed.”[51] Somewhat more than one hundred years later, this theory was confirmed by investigations made by the famous physicist Réaumur (1683–1757). Microscopic examination of cross sections of pearls show that they are built up of concentric laminæ similar, except in curvature, to those forming the nacreous portion of the shell. In a paper published by the French Academy of Science in 1717,[52] Réaumur noted this condition, and suggested that pearls are misplaced pieces of organized shell, and are formed from a secretion which overflows from the shell-forming organ or from a ruptured vessel connected therewith, and that the rupture or overflow is ordinarily produced by the intrusion of some foreign or irritating substance. Sir Edwin Arnold calls attention to this theory in his beautiful lines: Know you, perchance, how that poor formless wretch— The Oyster—gems his shallow moonlit chalice? Where the shell irks him, or the sea-sand frets, He sheds this lovely lustre on his grief. In pursuance of this idea, we find, in 1761, the Swedish naturalist Linnæus, “the father of natural history,” experimenting in the artificial production of pearls by the introduction of foreign bodies in the shell, and meeting with some degree of success. His discovery was rated so highly that it has been announced by some writers as the reason why the great naturalist received the patent of nobility, which is generally supposed to have been the reward for his services to science.