The chemical changes that take place in the panification of bread-flour, are by no means well understood. The saccharine mucilage, it appears, commences the fermentative chemical action that takes place in the dough, for without this substance, a mixture of flour, yeast, and water, cannot be made into true bread. The fermenting process when once commenced, is kept up by the gluten, forming the body of the paste through which the fecula and saccharine matter are diffused; and when the slight fermentation which it suffers, from changes in the saccharine matter, and supported by the presence of the gluten, has commenced, the paste becomes spongy and porous, from the disengagement of carbonic acid gas, while it still retains in some measure its elasticity; hence the lightness and porosity of well-baked wheaten bread; and hence bread, possessing these qualities, cannot be prepared from the flour of oats, barley, rye, or rice, or from any of the nutritive roots, as in all of these the quantity of gluten is considerably less, or entirely wanting, and no gluey elastic dough can be formed. The starch, which was merely diffused through the gluey dough, combines, during the baking, with a portion of water, into a stiff jelly, which renders the bread more digestible, and the gluten wholly disappears. A portion of carbonic acid gas, which becomes disengaged during the fermenting process, enlarges the bulk of the dough, which is thus rendered light, porous, and full of eyes, or cavities, in consequence of the extraction of the air bubbles, in the viscid glutenous matter; and the porosity of the bread is in proportion to the extent to which the rising of the dough is suffered to proceed.