A wad of sterilized cotton batting, packed into the mouth of the jar or tumbler, like a stopper, is sometimes employed, but it is not as effectual as the paraffin; for that, being poured in hot, sterilizes the surface of the jelly, thus killing any organisms that may have lodged upon it during the cooling. Organisms cannot go through batting; but, though it may be properly sterilized, it cannot be packed over the jelly until it has become firm, and during the time ferments may have settled upon it. Paraffin is a most satisfactory means of preserving jelly, and the only precaution necessary in using it is to put on two layers, the second one two or three hours after the first, or when all contraction has ceased. BREAD The two most practicable methods of making bread are with yeast, and with cream of tartar and bicarbonate of soda. Yeast is a micro-organism--an exceedingly minute form of plant life--which by its growth produces carbonic acid and alcohol. When this growth takes place in a mass of flour dough, the carbonic acid generated, in its effort to escape, puffs it up, but, owing to the viscous nature of the gluten, it is entangled and held within. Each little bubble of gas occupies a certain space. When the bread is baked, the walls around these spaces harden in the heat, and thus we get the porous loaf. Barley, rye, and some other grains would be very useful for bread if it were not that they lack sufficient gluten to entangle enough carbonic acid to render bread made from them light. Good bread cannot be made without good flour. There are two kinds usually to be found in market, namely _bread_ flour, and _pastry_ flour. The former is prepared in such a way that it contains more gluten than the latter. In making Pastry, or St. Louis flour, as it is sometimes called, the grain is crushed in such a manner that the starch, being most easily broken, becomes finer than the gluten, and in the process of bolting some of the latter is lost. For pastry and cake this kind is best. Lacking gluten, bread made from it is more tender, whiter, but less nutritious than that made from so-called _bread_ flour. New Process, or bread flour may be distinguished by the "feel," which is slightly granular rather than powdery, by its yellow color, and by the fact that it does not "cake" when squeezed in the hand; while St. Louis is white, powdery, and will "cake."