In some countries bleaks are pickled in the manner of anchovies. When of large size they are well flavoured, but they are too bony to be in much request as food, even by the poor. They are considered in greatest perfection in the autumn. ORDER VI.--CHONDROPTERIGIOUS FISH. 250. _The COMMON STURGEON_ (Acipenser sturio, Fig. 71), _is a large kind of sea-fish with five rows of bony tubercles along the body; the mouth beneath the head, and four fleshy beards betwixt the mouth and the extremity of the muzzle._ _This fish sometimes growes to the length of sixteen feet and upwards._ _It inhabits the European and American seas, and annually ascends the rivers in the early part of the year._ It is to this and to a still larger species of sturgeon called the BELUGA (_Acipenser huso_), which is found in the river Wolga, that we are indebted for much of the well-known substance called _isinglass_. The mode of making isinglass was long kept a secret by the Russians, and has only of late years been made public. This article consists of certain membranous parts of fishes deprived of their viscous quality and properly dried. The sounds, or air bladders, are those of which it is chiefly made. They are taken out, while sweet and fresh, slit open, washed from their slime, divested of a very thin membrane which envelopes them, and then left to stiffen in the air. After this they are formed into rolls, each about the thickness of the finger, and put into the shape in which we see them, by small wooden pegs, and left to dry. The kind called _cake isinglass_ is formed of bits and fragments put into a flat metal pan with very little water, heated just enough to make the parts adhere, and subsequently dried in the air. Although by far the greatest quantity of isinglass is obtained from the beluga, as being the largest and most abundant fish in the rivers of Muscovy, yet it has been ascertained that this substance may be made from the air-bladders of every species of fresh water fish. The principal consumption of isinglass is by brewers and others, for the fining of fermented liquors: this it appears to do merely by the mechanical effect of its organization, which forms a kind of strainer, or fine net-work, and carries the gross impurities before it, as it subsides. It is sometimes employed in medicine; and also in cookery, for making jellies, and other purposes. _Caviar_ is a kind of food made generally from the roes of the sturgeon. For this purpose they are washed, when fresh, by rubbing them, with the hands, in a sieve, to free them from the fibres by which the several eggs are connected together. They are then washed in white wine or vinegar, and spread out to dry. After some further processes, they are either formed into cakes, each about an inch in thickness and three or four inches in diameter, or they are packed in small kegs for use.