This brings us to a consideration of the digestibility of vegetables in general, which is always the paramount consideration when dealing with the value of any substance to be used as a food. It has been before remarked that young and vigorous persons seem to thrive on a dietary largely of vegetable character, but the case is certainly quite different with older people, particularly where their digestive powers are impaired. In the latter we often find that severe intestinal disturbances follow even after moderate indulgence in vegetable foods--particularly where they are served with vinegar, or some other fruit acid. Another peculiarity of foods of this kind that makes decidedly against their digestibility lies in the fact that, being soft and containing a large proportion of water, they are scarcely ever properly chewed, and as a consequence they are swallowed in comparatively large masses without having been adequately insalivated. Vegetables may be roughly classified as legumes, roots and tubers, and green vegetables, and will now be considered briefly in the order named. _Legumes,--Beans, Peas, Lentils, and Peanuts._--With the exception of the cereals, the legumes are the most valuable of all vegetable foods. Their nutritious properties are mainly due to their relatively high percentage of nitrogenous material, though they also contain starch and fat. Hence these vegetables contain the ingredients necessary to supply all the needs of the human economy; unfortunately, however, when eaten alone in sufficient bulk to furnish the nourishment required, they often--even in healthy individuals--give rise after a little time to dyspeptic disturbances.