Directions for mixing bread frequently tell you to "set a sponge." This is done by mixing all the ingredients except the flour, and then stirring into them just enough flour to make a thick batter. This mixture is set in a temperature between 70° and 90° and allowed to ferment. The "sponge" is a more watery mixture than dough and in it the yeast has an especially easy opportunity to develop. The setting of a sponge also serves as a test of the yeast. If the yeast does not greatly increase the quantity of the sponge and make it full of bubbles, it will not be strong enough to affect the stiffer dough. When the sponge has increased to about twice its size in the beginning, enough flour is stirred in to make kneading possible. The object of kneading is that the yeast may be distributed through the flour so evenly that its effect upon all parts of the dough will be the same. After the kneading the bread is "set to rise," that is it is put in a comfortably warm place, out of the way of draughts, and left while the yeast plants multiply and ferment the bread. When the dough has increased to about twice its original size, it is kneaded a little more, chiefly to break the bigger bubbles which would make holes in the bread. It is then moulded into loaves and rolls and set to rise again, this last because in the moulding it has acquired a little more flour and its sponginess has been somewhat compressed. It is finally baked, as has been said, to stop fermentation and preserve the porous character of the bread. Baking also forms the pleasant-flavoured crust. A person of inquiring mind may observe in the table of food values given in the previous chapter that the nourishing constituents are greater in quantity in flour than, with a slight exception in fat and ash, they are in bread. The natural question will then be, why take all this trouble to cultivate yeast plants in flour when the result furnishes less nourishment than flour? Why not mix flour and water and bake it? This would be "unleavened bread" which is somewhat like crackers, somewhat like macaroni, both of which register higher in nourishing constituents than bread. Nevertheless, they do not serve our purpose as well as bread, because they are much more hard to digest and more quickly create distaste. The body must not only have nourishment supplied to it, it must have it supplied in forms which it can use without serious difficulty. It is quite possible, therefore, to obtain more actual nourishment from digestible, appetizing bread which contains a smaller per cent. of nutriment, than from a crude and insipid flour mixture which contains a greater per cent.