The name _able_, or _ablette_, is given to several species of fish; but that which produces the pearl-essence is the _Cyprinus alburnus_, called in English the bleak. Professor Hermann, at Strasburg, was so kind as to send me one of these fish, which was caught there for the purpose of making pearl-essence, and which was dried so carefully that the species could with certainty be distinguished. It corresponded exactly with the figure given in Duhamel[786], which has almost a perfect resemblance to that given by Schoneveld[787]. May not the _alburnus_ mentioned by Ausonius among the inhabitants of the Moselle, be the same? At any rate, the bleak is to be found only in fresh water; and on account of its voracity bites readily at the hook. It is caught for the use of the French manufacturers in the Seine, the Loire, the Saone, the Rhine[788], and several other rivers. To obtain a pound of scales above 4000 fish are necessary; and these do not produce four ounces of pearl essence; so that from eighteen to twenty thousand are requisite to have a pound of it. In the Chalonnois, the fishermen get for a pound of washed scales fifteen, eighteen, and twenty-five livres. The fish, which are four inches in length, and which have not a very good taste, are sold at a cheap rate, after their scales have been scraped off. At St. John de Maizel, or Mezel, in the Chalonnois, there was a manufactory in which 10,000 pearls were made daily[789]. The first makers of these pearls must have laboured under a very great inconvenience, as they were acquainted with no method of preserving the fishy particles for any time. They were obliged to use the essence immediately, because it soon putrefied and contracted an intolerable stench. The great consumption, however, required that the scales should be brought from distant provinces. Attempts were made to preserve them in spirit of wine or brandy; but these liquors destroyed their lustre, and left them only a dull white colour. In the like manner brandy spoiled a real pearl, which, with the animal and the shell (_Mactra lutraria_), was sent to me by Dr. Taube, at Zell. It was therefore a very important discovery for this art that these animal particles can be kept for a long time in solution of ammonia, which is now alone used, and which perhaps could be used for many other purposes of the like kind.