Corn.— The seeds of the cerealia are not only the most important of all the varieties of veaetable food, but may even be ranked above alfother alimentary substances, animal as well as vegetable. The history of mankind suffi ciently attests the truth of this estimate,— an estunate which is confirmed by the appel lation of " the staff of life," that is applied to their chief product as prepared for food.
An inquiry into their composition explains this remarkable value, by showing that the nutriment which such seeds place at the dis posal of the vegetable embryo they contain, has a close resemblance to milk, both in the number and proportion of the alimentary principles of which it is composed.
The proteinous constituent of all the cereal grains forms a considerable proportion of their total weight. In wheat it even reaches 22 per cent. of the dried mass. But in rye, barley, oats, and maize, this amount is dimi nished to about 13 per cent. And in rice and buck wheat, it may be estimated at not more than 7 per cent. In respect to the varieties of protein which are present, we find sub stances resembling all three of its chief modi fications in the animal kingdom. Thus wheat contains a large quantity of vegetable gluten, and vegetable fibrin, which are respectively analogous to casein and fibrin; together with a small portion of vegetable albumen.
The anzylaceous or starchy constituent, which represents the calorific elements of the food, also N aries in quantity ; but to a smaller degree than does the protein. It forms about two-thirds of the fourfirst kinds of grain above mentioned. In maize and rice, however, it rises to about 78 and 86 per cent. respectively ; apparently replacing the protein which is diminished here. This starch is associated with a variable quantity of sugar, part of which may probably be regarded as produced from its own metamorphosis. And gum is also present in small quantity.
The hydrocarbons are only represented by a small quantity of fatty and resinous matter ; the greater part of which,together with the cel lulose also present, passes through the alimen tary canal without undergoing any digestion.
The salts found in the ash generally make up about 1 to 3 per cent. of the whole vege table mass. As regards their bases, they are chiefly characterized by containing little lime in comparison with magnesia. The quanti
ties of potash and soda experience great fluc tuations: — which are probably connected with the natural or artificial peculiarities of the soil in which the corn has been grown. The quantity of iron is generally considerable. As regards the acids of these salts, the phos phoric greatly predominates ; while the sul phuric is in but small quantity. And the chlorides, so important to digestion and nu trition, are almost absent.
The ordinary preparation of these different kinds of grain is such as to introduce some slight changes of composition. The grinding of corn into flour strips away the outer husk of the grain; and thus has the disadvantage of removing a part of it, which contains a much larger proportion of protein than its more starchy interior. The subsequent process of fermentation and baking converts part of the starch into sugar and alcohol, with the formation of carbonic acid gas. The slow extrication of this elastic fluid gives the bread a porous or spongy character ; which has the advantage of greatly increasing the effective surface that is subsequently exposed to the action of the digestive fluids. Part of the gluten of the flour is also lost in the process. But the whole amount of both gluten and starch which disappears is not ery consi derable; probably not more than 5 per cent. This trifling loss, and the addition of about 30 per cent. of water, constitute almost the only noticeable differences between the com position of pure wheaten bread, and that of the flour from which it is made. Their effect is, to exchange the composition already men tioned in speaking of wheat, for about 16 per cent. of protein, and 35 to 40 of starch, in bread of a moderate dryness. But the advan tages afforded by the spongy texture, and the intimate admixture of water, which are brought about in the process of making bread, are still further increased by. a mechanical change produced in the starch-granules themselves. For, under the influence of the moisture to which they are exposed, most of these swell up and burst, and thus place their contents in a state much more accessible to the changes which are subsequently induced in them by the salivary and pancreatic secre tions.