39^ 



NATURE 



[May 26, 192 1 



which they are composed (nacreous pearls, 

 columnar pearls, hypostracum pearls, perio- 

 stracum pearls, hinge pearls)". All these 

 classes, some valuable, some worthless, are, 

 from the biological point of view, pearls. Bio- 

 logically speaking, the Mikimoto pearl satisfies 

 all the conditions which go to make up a pearl as 

 defined above. It differs from a natural pearl 

 only in that it contains a foreign nucleus larger 

 than any foreign nucleus which I have so far 

 encountered in a natural pearl, and in that this 

 nucleus is a bead of mother-of-pearl such as does 

 not occur in Nature. Both these points could 

 easily be remedied. A smaller nucleus could be 

 introduced; or the nucleus might be removed 

 after grafting the sac in the oyster; or 

 a small natural pearl of inferior quality, or a con- 

 centrically crystallised bead of carbonate of lime, 

 could be used as a nucleus. A trade in the worth- 

 less pearls of Mytilus might even be revived for 

 this purpose ; according to Garner they were once 

 exported from this country to China for the 

 manufacture of "medicine." The somewhat 

 greater transparency, on the average, of Miki- 

 moto pearls, when compared with natural 

 pearls, could be remedied by either of these 

 processes. 



With regard to the question of distinguishing 

 the Mikimoto pearl without cutting it, much 

 vague talk as to scientific investigations has ap- 

 peared in the daily Press. Some of these investi- 

 gations remind me of the little boy who, having 

 learned that trains were propelled by steam, 

 lighted a fire in his go-cart, put a kettle on it, 

 and expected it to run by itself. Undoubtedly 

 experienced pearl merchants, and, indeed, any 

 zoologist who is familiar with the shells of the 

 different species and geographical races of pearl 

 and mother-of-pearl oysters, can usually distin- 

 guish pearls from the Japanese pearl oyster 

 (Margaritifera Martensii) from the pearls of other 

 species, just as they can distinguish Cevlon, 

 Australian, Central American, etc., pearls from 

 each other by slight differences in colour and 

 lustre; but this test only reveals that the pearls 

 come from the Japanese pearl oyster, and cannot 

 be used to distinguish naturally and artificially 

 produced Japanese pearls from each other; and it 

 would be useless for distinguishing pearls pro- 

 duced by the Japanese process in other species of 

 pearl oysters from pearls naturally produced by 

 the same species. 



This natural difference is greatly intensified 

 when the pearls are examined in ultra-violet light, 

 for which purpose an apparatus has been designed 

 and is already on the market. I hope shortly to 

 be able to examine some naturally produced 

 Japanese pearls with this apparatus. 'l anticipate 

 that they will agree with the artificially produced 

 Japanese pearls, and not with natural pearls from 

 other localities, as this test, like the rule-of- 

 thumb test based on the general colour and lustre, 

 NO. 2691, VOL. 107] 



appears to depend on the minute differences in the 

 structure of the nacre in different species and races 

 of pearl oysters. 



Immediately on the first announcement of the 

 presence ol these pearls in the market being made, 

 1 suggested to a Press representative who called 

 upon me that polarised light was the most hopeful 

 line along which to seek a test that would reveal 

 the presence of the artificial nucleus, and this 

 suggestion was published in one of the daily 

 papers on May 5. Immediately afterwards 

 1 got into communication with Mr. A. Bram- 

 mall, of the Imperial College of Science and 

 Technology, South Kensington, who has since 

 been engaged upon experiments which aim at 

 determining whether polarised light can be applied 

 to whole pearls in such a way as to furnish a 

 test. 



The behaviour of polarised light when passed 

 through sections of the natural and the Mikimoto 

 pearl respectively was a foregone conclusion 

 from our knowledge of the structure of their 

 centres. When examined with polarised light 

 between crossed Nicols, the section of a natural 

 pearl, of course, shows throughout the cross of 

 extinction characteristic of concentrically crystal- 

 lised bodies (except in those parts which are too 

 opaque to transmit light). A section of a Miki- 

 moto pearl, on the other hand, shows the four 

 arms of the cross in the outer part, which is con- 

 centrically laid down ; but the mother-of-pearl 

 bead appears alternately dark and light as the 

 slide is rotated, according as the part of the 

 exterior to which its laminae are parallel is in a 

 dark or a light sector. Mr. Brammall is not 

 yet in a position to make a definite statement as 

 to the practicability or otherwise of applying some 

 modification of this process to the whole pearl. 

 He will, of course, publish his results as soon as 

 they are completed. 



However, whether or not the pearls, produced 

 by the Mikimoto process, which are now on the 

 market, can be distinguished from naturally pro- 

 duced pearls, without destroying them, by virtue 

 of their containing a large bead of mother-of- 

 pearl, which behaves differently towards polarised 

 light or towards some other variety of light, 

 Mr. Mikimoto can easily remedy this in future by 

 a modification of his process, such, for example, 

 as one of those suggested above. That being so, 

 and having in view the fact that, in the appro- 

 priate localities, "Oriental," Australian, Central 

 American, and other varieties of pearls could be 

 produced by the same process, it is probable that, 

 as time goes on, more and more of the pearls 

 coming into the market will have been produced, 

 not by the old-fashioned methods of fishing for 

 the "wild" pearl oyster, some of which methods 

 have existed almost unchanged from time imme- 

 morial, but by such applications of scientific 

 knowledge to cultivated pearl oysters as that 

 in which Japan has given so conspicuous a 

 lead. 



