Carbonates and Salts include chloride of sodium, or common salt, as well as potash, phosphates of lime, and iron. Common salt is a necessary food, but the fact is that many persons now-a-days get too much of it in the form of salt fish and flesh. It is the only mineral habitually added to food as such. Potash salts we find in all fresh fruits and vegetables. Probably no defect in diet is more common than a want of these, especially in our large towns. Lime is necessary for the building up of bones and teeth. We look for it in milk for the young, and in whole grains, and we know that it has been missing when we see weak and distorted limbs and broken teeth. Iron is generally thought of as a physic and not as a food. It is, however, a necessary constituent of the blood, and is chiefly derived in an organized form from fresh vegetables. It is also largely present in many natural tonic waters.
Starch or floury Foods are the cheapest and most abundant of all, so that if people have enough of any food they are likely to have enough of these. Over-fed persons are an exception to this rule, for too small a proportion of their diet is starchy. Bread, potatoes, rice, barley and all the floury foods contain more starch than anything else, and cornflour, arrowroot, sago and tapioca are nearly pure starches. There is much starch too in beans, peas and lentils, though they are generally spoken of as albuminoids, or flesh-forming foods, because of the very large amount of legumin that they contain. There is no starch in milk, but there is sugar, which replaces it. An infant can make no use of starchy food, having no power to digest it. Heated to 200° or 400° starch becomes dextrine, known too as "British Gum." The crust of a loaf, biscuits and baked flour all show dextrine.
Sugar and treacle are good foods and substitutes for starch. They are, however, apt to produce acidity in grown-up persons if used too freely, though children can and do eat large quantities without inconvenience.
The fats, starches and sugars are called heat-producers, because they are oxidized or burnt in the body to keep up the temperature to its proper degree. From the starches and sugars fat is deposited, if more is consumed than is required to maintain the heat of the body; therefore, the way to get thin is to eat little or none of these, or, better still, to take plenty of exercise and let them become completely oxidized.
Fat.—Fat, whether it is in the form of butter, cream, dripping, meat, bacon, oil, or by any other name, is necessary for food, and many are the persons that suffer in health from want of it, especially among the poor, who cannot afford the dearer fats, or do not know the cheaper, and among the sickly, who cannot—or fancy they cannot—digest fat in any form. If it can be digested one fat is as good a food as another. Cod-liver oil and cream are the easiest to digest. Fats that are greatly heated decompose, and are always difficult of digestion, which is the reason why fried food often disagrees. Many persons, who cannot eat a lump of fat with meat hot or cold, can eat buttered toast,
