英文科學(xué)讀本 第五冊·Lesson 46 Fresh Vegetables and Fruit

Lesson 46 Fresh Vegetables and Fruit

Under the name of fresh vegetables we include tubers, such as the potato; fleshy roots, such as the turnip, carrot, parsnip, and radish; as well as green vegetables, such as the cabbage family, lettuce, spinach, cauliflower, water-cress, onion, etc.

These, like all vegetable food, contain both flesh-forming and heat-giving matter in various proportions. The potato, although it contains little or no nutriment for tissue-forming, is a very valuable heat-giving food. Nearly all its solid matter consists of starch.

Carrots, turnips, parsnips, cabbages, cauliflowers, and onions are very nutritious, both as tissue-formers and heat-givers. If one of these fresh vegetables—say a potato, a turnip, a cabbage, or a cauliflower—were placed over a fire, or in an oven, it would at once begin to give off vapor, and after a time it would gradually dry and shrivel up.

If we weighed it before and afterwards, we should find a great difference in its weight. The potato, for instance, would lose about 75 percent of its weight by this drying process; the turnip no less than 90 percent. It is clear then that all these fresh vegetables contain a large amount of water. Whence did they get this water?

It was absorbed from the soil by the roots of the growing plant. Now water, as we know, acts as a solvent, and dissolves the mineral matters out of the soil. The roots of the plant, in taking up the water from the soil, take up also the mineral matters, which that water holds in solution, and these mineral matters are absorbed into the structures of the growing plant with the water.

Let us now take our potato, dried as it is, and burn it. Of course most of its substance will be consumed with the burning, but in the end we shall have a residue, which will not burn, which no amount of heat can consume. It remains as an ash after the burning. This ash represents the mineral matter which was taken up from the soil by the roots of the plant.

It is more perhaps for their value as storehouses of mineral matter, than for their other properties, that fresh vegetables are so important to our health and well-being.

It is a common occurrence that people who have been deprived for any length of time of fresh vegetables, develop scurvy and other skin diseases.

One important mineral, potash, is always found in some form or other in carrots, turnips, parsnips, radishes, asparagus, watercress, lettuce, and endive. Potash is chiefly valuable as a preventive of scurvy and other eruptions of the skin, or, as scientific men would say, for its anti-scorbutic properties.

Soda, lime, common salt, and the salts known as phosphates are all equally necessary to our general health and well-being. They find their way into our system by the same means, and from the same source.

Fruit, of all kinds, although it possesses a very small amount of nutritive matter, is nevertheless of great value as food, because, in addition to the sugar which it contains, it is a storehouse for certain mineral matters and acid juices. As we saw in the case of the vegetables, the mineral matters are valuable as anti-scorbutics; the acid juices are equally valuable in medicinal properties.

No fruit can be safely eaten, however, in an unripe state, for then the acid juices are very powerful, and would quickly be the cause of indigestion and other derangements of the system. Unripe fruit should never be eaten unless cooked; unsound fruit should never be eaten cooked or raw. On the other hand, fruit, when it is ripe and sound, forms a pleasant and agreeable change of diet, and ought to occupy an important place in the meals of the day.