The various leguminous seeds contain a quantity of the protein-compounds which may be estitnated as forming, on an average, nearly 30 per cent. of their weight ; or half as much again as that present in the cerealia. The quantity of their starchy constituent is, how ever, much less ; being barely 40 per cent. They contain a somewhat larger quantity of gum. They have also a larger (31) per centage of saline ash ; the several ingredients of which, though almost identical with those of the cerealia, approach each other much more nearly in quantity. From the few analyses hitherto made, it would appear that the quantity of alkaline bases is very large : but that potash pre dominates over soda ; and lime nearly equals magnesia. And though the phosphoric is still the predominant acid, sulphuric and hydro chloric are also combined with the above bases : — the latter chiefly with soda.
The value of these vegetables as food will of course depend on the preparation to which they have been subjected before being eaten. When ripe and dried, their small proportion of water, and their great density, together with the little surface they expose, together render them almost impregnable to the attacks of the various digestive agents. And even after moderate mastication, their larger fragments pass with little change through the whole of the intestinal human canal.
But after careful boiling, which bursts their starch granules, dissolves their gum, and softens and breaks up their various tissues, they assume the proper digestive value to which their composition entitles them. So prepared for eating, their large constituent of vegetable casein renders them a most efficacious azotized food. While their con siderable quantity of starch, as well as their comparatively uniform admixture of the par ticular salts most important to nutrition, gives them a completeness for dietetic pur poses, which even wheat can scarcely be said to possess. Hence we are entitled to sup pose that, if suitably prepared by cooking, some of these legumes might form a food sufficient for the maintenance of health.* At any rate, we may presume, that their dietetic usefulness is rather under than over rated ; so that, on physiological grounds, their consumption as human food might be advan tageously extended far beyond those limits which the custom of modern European na tions (and especially of the English) seems to have assigned them.
The potato, the starchy tuber of a plant belonging to the poisonous genus of the So lanece, is an article of vegetable food, the pro perties of which render it a remarkable con trast to the preceding group. We may best sum up its average composition as consisting of about 75 per cent. of water, and 25 of solids. Of the latter portion, only one-tenth is composed of protein, which is present in the form of albumen and asparagin. Three fifths of these solids are starch. The salts of its ash amount to about 1 per cent. They are
chiefly characterized by the fact, that though they contain little lime, and scarcely any soda, they include a large amount of potash ; which, in the fresh tuber, is probably com bined with some of the organic acids present. The quantity of phosphates is also very small :— barely, one-fourth of that contained in the various cerealia.
The above sketch of the composition of this vegetable sufficiently entitles the physio logist to range himself with the economist in determined opposition to the predominant use of this vegetable as the principal arti cle of food. We may dismiss from our notice all consideration of the social and moral degradation which, since its introduction with this object, have steadily followed such undue use of the potato as the staple ali ment in various parts of Europe. We may even set aside those fearful outbreaks of pestilence in Ireland which, though produced by the quantitative failure of one crop, must surely have been in some degree fostered by a peculiar state of the constitution — itself probably founded, in part, on the qualitative deficiencies of the previous food. Our ob jections to the potato find a better excuse in such a composition as the above. Rough as is the above estimate, it nevertheless claims to be based upon analyses of unusual number and accuracy. It shows that the food to which it refers is wanting in some of the most important saline constituents of the body;—such as the phosphates, which are hourly leaving the organism in comparatively large quantity. And that, in addition to this grave fault, it contains so small a proportion of protein, that we may calculate about thir teen pounds of potatoes as the quantity which a man ought to take into his stomach, in order to replace the waste of his body by a sufficient quantity of the histogenetic con stituent of the food. At least this would be the amount corresponding to the protein which long experience has shown to be enough, and not too much, for the daily ration of a soldier : that is, for the food of an adult male, in good health, and habituated to moderate, but not excessive, bodily labour. Lastly, we need hardly add, that the form and arrange ment of the protein contained in the potato are such as would scarcely ever allow it to be as well digested as the protein contained in the bread and meat of the soldier's ration. Hence its less suitable quality would require to be compensated by a still further increase of quantity.* But the mixture of potatoes with other alimentary substances, and especially with meat or milk, removes all these objections, and restores it to its proper rank in the scale of food. While its saline constituents, its potash, and its organic acids, admirably adapt it for that use as an anti-scorbutic which experience points out as one of its most valuable qualities.