May 26, 192 1] 



NATURE 



397 



(such as a grain of sand) is present, consists 

 throug-hout of concentrically deposited layers, 

 which differ in degree of transparency or opacity 

 in different specimens (Fig. i). The Mikimoto 

 pearl, in its outer layers, has the same structure 

 as the natural pearl, but has an artificially manu- 

 factured bead of mother-of-pearl, composed of flat 

 parallel laminae of nacre, in its centre (Fig. 2). 

 (These preparations and photos were made 

 under the supervision of Mr. Brammall, 

 to whose investigations reference is made 

 below. ) 



The method by which Mr. Mikimoto produces 

 these pearls has been patented by him in Japan 

 and other countries, and an application for a 

 British patent has already been filed, and is open 

 for inspection at the Patent Oflfice. The informa- 

 tion here given was obtained from this specifica- 

 tion, from a short description and figure published 

 in one of Mr. Mikimoto 's catalogues, and from 

 facts supplied by Mr. Toranosuke Kato, his 

 London representative. The process involves the 

 most delicate and skilful manipulation, and it 

 could be carried out, presumably, onlv bv care- 

 fully selected and trained workers. The shell is 

 removed from one pearl oyster, and a bead of 

 nacre or other suitable nucleus is laid on the outer 

 shell-secreting epidermis of the mantle. This 

 epidermis, which is composed of a single laver of 

 cells of microscopic size, is then dissected off the 

 oyster, and made to envelop the nucleus as a sac, 

 the neck of which is ligatured. This sac is then 

 transplanted into a second oyster and embedded 

 in its sub-epidermal tissues, the ligature is re- 

 moved, certain astringents or other reagents are 

 applied to the wound, and the second oyster, with 

 its grafted pearl sac contaming- the mother-of 

 pearl bead, is returned to the sea, where it has 

 to remain for several vears before a coating of 

 pearl of suflFicient thickness is secreted around 

 the introduced bead. (In his letter of May 30, 

 1914, Mr. Ikeda stated that it took seven 

 years.) 



Now Mr. Mikimoto 's success is based on the 

 fact, which follows from my work in 1902,1 and 

 was further demonstrated by Alverdes's re- 

 markable experiments ten years later,^ that it is 

 not the presence of an irritatins; intrusive body 

 that determines the formation of a pearl, hut the 

 presence in the suh-epidermal tissues of the oyster 

 of a closed sac of the shell- secretinfr epidermis. 

 the secreting surface of which is not continuous 

 with the secreting surface of the epidermis which 

 lays down the shell ; and that unless this epidermal 

 sac is introduced by transplantation (as in 

 Alverdes's and Mikimoto's methods), or is induced 

 by the specific stimulation of a particular kind of 

 parasite (as in the pearls in Mytilus caused bv the 

 trematode Gymnophallus), or arises by some still 



J Jameson, Proceedings of the Zoological Society, 1902, vol. i., pp. 140-^6, 

 and Nature, January 22. 190?, p. 280. 



2 F. Alverdes, " Versiiche Tiber die kunstiche F-rae'-gune von Mantelperlen 

 ber Susswassermuschein," Zoof. Ameiger, vol. xlii., No. i', 1913, pp. 

 441-58. 



NO. 2691, VOL. 107] 



unknown cause or causes (as in the Ceylon pearl 

 oyster), no irritating body introduced into the 

 shell or tissues* can be expected to become the 

 nucleus of a pearl. In my" 1912 paper ^ I showed 

 that the vast majority of pearls from the true 

 pearl and mother-of-pearl oysters have no recog- 

 nisable nuclei of foreign origin, the bodies so 

 often taken for such, like the dark portion of the 

 pearl shown in Fig. i, and the centre of the pearl 

 diagrammatically shown in Fig. 3, being- com- 

 posed of a kind of shell substance of pathological 

 origin, identical with that with which the oyster 

 repairs an injury to its shell.* On the other hand, 

 some of the natural pearls I have examined con- 

 tained foreign bodies which (apart from the special 

 case of the trematode which causes pearl sacs 

 to form in Mytilus) ranged from diatoms and 

 fragments of radiolarian shells and sponge 

 spicules to quartz grains measuring, in one case, 

 as much as 08 mm. in diameter. I propose 

 to outline a theory attempting to account 

 for the presence of these bodies in a later 

 paper. 



From the biological aspect there are two 

 classes of pearly bodies. For the first of these, to 

 distinguish them from true pearls, I adopted the 

 name "blisters," familiar to pearl fishers, in 1902. 

 Blisters (Fig. 3, hi.) are excrescences on the in- 

 terior of the shell formed to close holes made by 

 shell-boring animals, or to coat over intrusive 

 objects such as grains of sand, small crabs, Fier- 

 asfer, etc., and, in the case of the Buddha 

 "pearls," Linnaeus's "pearls," and the "half 

 pearls " originally produced bv Mr. Mikimoto, 

 metal images or beads. Over such a blister the 

 epidermis forms a little pocket, directly continuous 

 with the shell-secreting epithelium. A pearl, on 

 the other hand (Fig. 3, p.), is formed in a 

 closed sac of shell-secreting- epidermis, which is 

 embedded in the tissues of the oyster, and the 

 nacre-secreting^ surface of which is not continuous 

 with that of the epidermis that lays down the 

 shell itself. A blister is a more or less hemi- 

 spherical body passing over on all sides into the 

 shell substance ; a pearl is a concentrically 

 deposited body, the substance of which is no- 

 where continuous with that of the shell. A pearl 

 may, in the course of time, be ejected into the 

 space between mantle and shell, and become more 

 or less buried in the shell, forming the core 

 of a blister; but in that case it can be 

 dissected out from the shell layers deposited 

 over it. 



The trade distinguishes different kinds of pearls 

 according- to shape and size (fine pearls, baroque 

 pearls, seed pearls, etc.), just as biologists dis- 

 tinguish certain classes according to where they 

 arise (parenchyma or mantle pearls, muscle 

 pearls), or to the kind of shell material of 



■■'Jameson, Proceedings of tbe Zoological Society, 1912, pp. 260-358. 



* 't is astnnishine how the "foreien nurleus" theory of pearl formation 

 sticks, as witness the utterances of scientific men of standing which have 

 been called forth by the recent announcement. 



