20 U, S. BUREAU OF FISHEETES 



substances are often found in surprisingly large quantities under 

 normal conditions in many of the lower orders of animals. Not being 

 eliminated, they are disposed of as deposits in out-of-the-way places 

 among the tissues. Urea accumulates in sharks and rays, uric acid 

 and urates are in certain snakes and butterflies, and among inverte- 

 brates generally extensive accumulations of this kind are of frequent 

 or regular occurrence. 



Ewald and Krukenberg (1882 and 1883) found guanin in the skin 

 of chameleons and lizards, in alligators, snakes, frogs, snails, fishes, 

 and many other animals. The tissues containing it are the skin, 

 connective tissue, retina, iris, peritoneum, air bladder, liver, pan- 

 creas, etc. It is found in the excrement of spiders and certain snakes, 

 and is abundant in the bird guano deposits of Peru and elsewhere. 

 With the possible exception of those in the iris of frogs' eyes, these 

 deposits are all amorphous, and it is only in the fishes that crystalline 

 deposits are found to any considerable extent. Of course, the 

 crystalline state is absolutely essential for purposes of making pearl 

 essence. 



GUANIN IN FISHES 



In the fishes guanin is put to the useful purpose of camouflage. 

 Most of it is deposited on the belly side of the fish and makes a bright 

 silvery appearance to blend with the bright sky as seen from below 

 by enemies of the fish. Similarly, when seen from above the fish is 

 a greenish gray to blend with the color of the water. 



This guanin deposit is present in abundance in a vast number of 

 species of fish; in fact, the exceptions are those without visible depos- 

 its of guanin. Our familiar herrings, sardines, whitefishes, men- 

 haden, mackerel, sahnons, butterfish, carp, sunfishes, tarpon, scup, 

 squeteague, ladyfishes, spot, croakers, hogfish, barracuda, bonito, 

 shad, gizzard shad, mullet, and many others exhibit the silvery 

 luster. It is even doubtful that any fish exist which are free from 

 guanin deposits. Such fishes as haddock, cod, and flounders have 

 subdermal connective tissues heavily charged with amovphous gua- 

 nin, which is chalky white. It is of zoological interest to note that 

 these species that live on the bottom and have amorphous guanin 

 do not need the lustrous camouflage that would be provided b}^ the 

 crystal variety. It is not sufficient to say that pearl essence is a 

 suspension of guanin — it must be in a definite crystalline form. 



EUROPEAN SOURCES OF PEARL ESSENCE 



The European fish from which pearl essence has been made from 

 the seventeenth century is the bleak (German, Ulcelei, Lauhe; 

 French, ahlette), Alhurnus lucidus, a small fish of the carp or minnow 

 family (Cyprinidfe), widely distributed in the fresh- water streams of 

 Europe. The fish is of no value as food and serves only the one pur- 

 pose of producing pearl essence. This fish serves particularly well 

 as a source of pearl essence because it is small and comparatively 

 poor in dark skin pigments that would discolor the essence. In 

 England essence is made from the herring {Clwpea Jiarengus). It is 

 understood that there is a plant manufacturing it at Peterborough. 



In Europe there is a commerce of some importance in the scales 

 of the ahlette, carried on by producers who sell the mildly preserved 



