116 PEARLS [CH. 



Rubbel in the freshwater mussel, will be discovered 

 in the case of the Ceylon oyster. 



Thus we have seen how pearls may be caused by 

 foreign bodies (sand grains, parasites, or other objects) 

 or by internal products of the pearl-producing mollusc. 

 As Dubois, in a recent summary of the matter, puts 

 it : " II existe deux categories de margaritose on 

 maladie perliere; I'une parasitaire et I'autre non 

 parasitaire." 



The importance of the causes referred to varies 

 according to the species of shellfish in which the 

 pearls are found, but whichever cause we look into, 

 we find something of the romance of science, a know- 

 ledge of which cannot fail to increase the value of 

 the pearl as a gem, in the eyes of any enlightened 

 owner. 



CHAPTER IX 



PEARLS IN JEWELLERY AND TRADE GENERALLY. 

 ODD FACTS 



It will have become evident from the preceding 

 chapters that the pearl is still retaining its hold in 

 the fashionable world of the 20th century. As a 

 matter of fact, the value of pearls has steadily 



