an excessive quantity of proteid, a proceeding entailing waste and exhaustion of the digestive apparatus, the balance must be made up by eating carbohydrate.
The forms in which people are most familiar with carbohydrate are starch and sugar. Sugar is the better food, as it is so much more soluble than starch; and, in fact, starch is always turned into a kind of sugar before it is used by the body. The common cane-sugar, which everyone knows so well, is about the most useful food we have, owing to its purity, and therefore concentration, and its simplicity. A very small amount of digestion is necessary to convert it into the simplest of all carbohydrates, a substance easily stored, as glycogen, till wanted, which is present in muscle after a meal, and is used up when the muscle is active, being oxidized to carbonic acid gas, sarcolactic acid, and alcohol.
The importance of carbon in the diet is therefore obvious; and people who intend doing extra muscular work should take extra sugary food rather than extra proteid. A locomotive which is about to make a record run takes in more coal, not more engine-drivers, and our athletes now follow the same principle. We shall, however, have a good deal more to say about athletes presently.
There is yet another point to be considered in respect to carbon. Carbon need not be taken in the form of carbohydrate, the alternative being fats and oils. Fats and carbohydrates are both composed of the elements carbon, hydrogen, and oxygen, but the proportions in which they are joined are different. Fats are not such useful foods as carbohydrates, nor to most people so pleasant—compare a spoonful of olive-oil and a lump of sugar. But there is one important point to be urged in their favour: they yield twice as much heat as either proteids or carbohydrates; so their position among foods is assured.
The other chemical necessities of the body we need only mention here. Hydrogen is one of the components of proteid, carbohydrate, fat, and water; and if it does not enter in the last form, it—at any rate, most of it—leaves as such, being oxidized in the tissues. Sulphur and iron deserve honourable mention; common salt is
