for human food, and use them only for feeding the animals which supply us with meat. As far as common experience affords evidence, white bread should be more serviceable than brown, since it is invariably preferred by the working classes, of whose food it forms so large a proportion. Still it is possible that this may be merely a preference for the taste and appearance of white bread. Whatever may ultimately turn out to be the truth on this point, the corn which contains the largest amount of starch or white flour has a higher market value than that which contains the largest amount of gluten. This will be apparent from the table furnished by Dr. Odling.

Note.-Nos. I, and II. are fine well-conditioned flours; No. III. a cheap inferior flour; No. IV. a very much damaged flour.

Thus what is supposed to be the heat-forming portion of the food is more esteemed than that portion which is supposed to form flesh. With regard to the extractives,' says Dr. Odling, 'I think I may safely say that they are inversely proportionate to the good condition of the flour. A high percentage of extractives nearly always indicates some defect in the harvesting or storing of the flour.'

From a Memoir of Messrs. Lawes and Gilbert we extract a Table, which shows how much of each description of meal is obtained by dressing good wheat.

The first column of figures contains the proportion of each kind

of

of flour or meal derived from one hundred parts of wheat. The second column gives the amount of solid matter per cent. in each product, after the water originally contained in it had been drawn off by heating. The third column contains the amount of mineral ash remaining after samples were completely burnt. And the fourth column states the percentage of nitrogen. Here again it appears that the coarser parts, rejected in ordinary breadmaking, contain the largest amount of nitrogenous matter.

In pursuing the examination of the structure of wheat it is found that the nitrogenous constituents do not consist simply of gluten, the form insoluble in water, but that there exists, especially in the outer layers, which form the mass of the bran, an albuminous substance soluble in water, called by M. MègeMouriès, who first pointed out its peculiarities, cerealine. It is found that its presence causes increased fermentation, and under particular circumstances renders bread soft, heavy, sour, and of bad quality. Nor is this all. Owing to its own decomposition and the influence it exerts in altering the accompanying gluten, it may leave even less nitrogenous matter in the finished loaf than when the bread is made with finer flour. To make these matters clear, we must now pass to the examination of the operations by which the flour is converted into bread.

When flour and water are mixed together, the glutinous matter associated with the starch causes the whole to cohere, and thus forms a paste. Pure starch, as we see in the case of arrowroot, settles down in the shape of powder to the bottom of cold water, because none of the cementing gluten is present. Dough would form a dense solid mass when baked, if in the process of making it a quantity of air were not diffused throughout the mass, the expansion of which by the heat of the oven renders the substance more or less porous. In pastry the crust is further lightened by the use of butter, which acts by its particles melting so as to leave cavities. The 'lightening' by the use of eggs is partly attributable to the increased viscidity arising from the albumen of the egg, which thus assists to confine the air-bubbles in the substance. Carbonate of ammonia (or salt of hartshorn), which entirely evaporates in baking, is used in confectionary to raise the paste by the bubbles it forms in volatilization. The 'unfermented' breads are rendered light upon the same principle: the usual method is to mix soda with the flour, and hydrochloric acid with the water, in the proportions in which they unite to form chloride of sodium or common salt. The effervescence, like that produced in mixing Seidlitz powders, converts the paste into a porous sponge, which, however, requires to be very quickly placed in the oven. The 'salt' formed by the mixture replaces that ordinarily added to

the

the dough in making bread. Whatever, therefore, be the method by which bread is made light, the object to be attained is to pervade the substance with numerous cavities which keep the particles of flour asunder instead of forming a compact and unyielding mass.

The science which gave an insight into the cause of the 'rising' of bread, and suggested substitutes for the ordinary fermenting materials, is but of recent date. These ferments operate by generating an infinity of gas bubbles, which honeycomb the dough. The earliest process was to employ leaven, which is largely used still in the manufacture of the black ryebread of the Continent, and consists of dough which has become more or less sour by over-fermentation. This is kept from one baking to another, to 'inoculate' a fresh bulk of paste with its fermenting influence. No sooner does it come in contact with the fresh dough than it communicates its own properties as by contagion. Probably the discovery of leavening has been owing to accident in many countries through neglected paste having been attacked by the fungus which is the cause of the fermentation. The substitution of the purer and more controllable 'essence,' the yeast, upon which the entire operation depends, is of comparatively recent date. Leaven contains yeast in a state of activity, mixed with partially decomposed flour. The yeast causes a decomposition of the constituents of flour, and changes a portion of its starch into sugar, and next into carbonic acid gas, which converts the mass of dough into a sponge. 'Brewers' yeast' and 'German yeast' are the ordinary forms in which this substance is used; the former is derived from beer, and German yeast is the same product 'grown' in infusions of malt especially made for the purpose, and hence not contaminated with the bitters which accompany brewers' yeast, and render it necessary to wash it very thoroughly with water before using it for making bread.

The simplest method of preparing the dough is to mix the yeast carefully with a part of the water required, to stir this into the centre of the mass of flour, and then add more liquid until the whole is converted by kneading into a firm but flexible paste. This is put into a warm place until it has swollen to twice its original size, is once more kneaded, is then left again to rise, and is finally parted into loaves, and transferred to the oven. The object of the kneadings is to mix the materials, and to distribute the yeast equably through every portion of the mass. The purpose of letting the dough stand is to give time for the fermentation to be continued until sufficient carbonic acid has been generated.

The

The mode we have just described of 'setting a sponge' is somewhat varied in ordinary practice. A process commonly employed in home-baking is to mix the yeast smoothly with a small quantity of gently-warmed water (sometimes a little milk is added, which promotes fermentation), and pour the compound into a hole made in the middle of the flour. A portion of the flour is next stirred into the liquid and a further portion strewed over the top. When left in a warm place, fermentation goes on, and the bubbles raise the sponge through the top coating of flour. The whole is then kneaded together with the addition of the requisite quantity of water, and left once more to rise. The kneading is again repeated, after which the dough is formed into loaves, and these are left till they have swelled to double their primitive size, when they are put into the oven. The object in this plan is to be certain of a good fermentation in a stage of the process when there is still time to add more yeast, that is before the kneading is completed. Those who prepare bread in large quantities for sale, carry out the principle of the sponge' or leaven in a still more complicated fashion, the flour and water being added, with additional yeast, in successive relays, at intervals of several hours. Instead of the addition of milk to the yeast, a cheaper substitute is said to be extensively used by bakers in setting the first sponge. This is a thickish paste made by mashing boiled potatoes with water, which from the softened condition of its starchy contents is more readily attacked by the ferment than pure flour.

Yeast is known to most persons merely as a creamy liquid, or in the German yeast as a tough semi-solid matter, which softens when placed in water. When the dough, through its influence, 'rises into a spongy mass, it may be compared to a species of solidified froth. Froth arises from the entanglement of particles of air or other gaseous matter in a more or less viscid liquid. The air confined in soda-water' is a gas dissolved in pure water; when the pressure is removed it escapes very rapidly, so that no permanent froth is produced. In bottled beer and ginger beer, the carbonic acid does not escape so freely, since the liquids possess a certain viscidity which retains the gas in bubbles. We cannot blow bubbles from pure water, but soap and water is sufficiently tenacious for the purpose. The cavities or bubbles in dough are produced exactly in the same way as those of the froth of bottled beer or other effervescing liquid; but two circumstances concur in bread to render them permanent; first, the fact that they are slowly formed; secondly, that they are generated in a substance which, while it is soft enough to allow the bubbles to expand, is tough enough to retain them. One of the main objections to what is called unfermented bread,' in which the

lightness

lightness is produced by simple effervescence, arises from the sudden liberation of the gas on mixing the acidulated water with the flour containing a carbonated alkali. It becomes necessary to place the bread immediately in the oven, or its spongy character disappears.

It will surprise many persons to be told that yeast is a plant. It belongs to the class of Fungi, and in accordance with the general habit of its kind it differs from the green forms of vegetable life by feeding upon organic substances. The vegetative structures, mostly colourless and often undistinguishable without the aid of the microscope, are in many cases extraordinarily developed when their presence is hardly suspected except by the botanist. Gardeners are aware that the productiveness of their mushroom-beds is dependent on the healthy development of a mass of 'spawn,' of which the mushrooms are the fruit; but many persons are ignorant that the toad-stools upon rotten wood are the mere indices of an invisible but widely-spreading spawn carrying destruction in the form of 'dry-rot' as it extends itself among the fibres of the wood. Again, the appearance of moulds and mildews upon preserved vegetable substances or liquids is an index that the mischief is far advanced; for these are but the fruits of the fungi, produced in most cases only after the vegetative structure ('mother,' flocculent clouds, and the like) has extensively spread.

The Yeast-plant represents one condition of a species of fungus remarkable for the diversity of forms it exhibits, its wide, nay, universal distribution, and the magnitude of the effects, sometimes beneficial, sometimes mischievous, which it is capable of producing. The forms in which it is familiar to most persons, although its nature may be unsuspected, are yeast, the gelatinous vinegar-plant, the mother' of vinegar and many decomposing vegetable infusions, and the common blue or green mould' (Penicillium glaucum) which occurs everywhere on sour paste, decaying fruits, and in general on all dead organic matters exposed to combined moisture and moderate heat. Yeast and the Vinegar-plant are the forms in which it vegetates, under various circumstances, when well supplied with food. Mildew is its fruit, formed on the surfaces exposed to air, at certain epochs, like the flowers and seeds of the higher plants, to enable it to diffuse itself, which it does most effectually, for the microscopic germs, invisible singly to the unaided sight, are produced in myriads, and are so diminutive that ordinary motes floating in the atmosphere are large in comparison. When we know that the pollen-dust of fir-trees, which consists of particles upwards of six times the diameter of the spores of this mildew,

sometimes