The elements which we require in order to supply the daily waste of the mineral constituents of the body are contained in greater or less quantities in nearly all the articles which man uses for food. But it may readily happen that, by adopting an ill-regulated diet, a man may not take a sufficient quantity of these important elements. It must also be noticed that articles of food, both animal and vegetable, may be deprived of a large proportion of their mineral elements by boiling; and if, as often happens, the water in which the food has been boiled is thrown away, injurious effects can scarcely fail to result from the free use of food which has lost so important a portion of its constituent elements. Accordingly, when persons partake much of boiled meat, they should either consume the broth with the meat, or use it as soup on the alternate days. Vegetables steamed in small quantities of water (this water being taken with them), also afford a valuable addition to boiled meat. In fact, experience seems to have suggested the advantage of mixing carrots, parsnips, turnips, and greens with boiled meat; but unfortunately the addition is not always made in a proper manner. If the vegetables are boiled separately in large quantities of water, and served up after this water has been thrown away, more harm than good is done by the addition; since the appetite is satisfied with comparatively useless food, instead of being left free to choose, as it might otherwise do, such forms of food as would best supply the requirements of the system. Salads and uncooked fruits, for instance, contain saline ingredients in large proportion, and could be used advantageously after a meal of boiled meat. Potatoes are likewise a valuable article of food on account of the mineral elements contained in them. And there can be no doubt that the value of potatoes as an article of food is largely increased when they are cooked in their skins, after the Irish fashion.
Lastly, we must consider those articles of food which promote the natural vital changes, but do not themselves come to form part of the frame, or, at least, not in any large proportion of their bulk. Such are tea, coffee, and cocoa: alchoholic drinks; narcotics; and lastly, spices and condiments. We may compare the use of these articles of food to that of oil in lubricating various parts of a steam-engine. For, as the oil neither forms part of the heat-supply nor of the force-supply of the steam-engine, nor is used to replace the worn material of its structure, yet serves to render the movements of the machine more equable and effective, so the forms of food we are considering are neither heat-producing nor flesh-forming, nor do they serve to replace, to any great extent, the mineral constituents of the body, yet they produce a sense of refreshment accompanied with renewed vigour. It is difficult to determine in what precise way these effects are produced, but no doubt can exist as to the fact that they are really attributable to the forms of food to which we have assigned them.