英文科學(xué)讀本 第五冊(cè)·Lesson 41 Leguminous Foods

Lesson 41 Leguminous Foods

I have here some peas, and a few different sorts of beans, said Mr. Wilson. "We sometimes speak of these things under the common name of pulse. The Latin name for them is legumen, and this is why they are always described as leguminous foods.

You have no doubt seen these things growing, and you know that they are the seeds of the plants which produce them. The fruit of the plant is, in every case, a pod, and these seeds are arranged in regular order in the pod. Our business now is not with the plants, but with these seeds. We want to learn something of their value as food material. Have you ever eaten some fresh, young, green peas? If you have, you can tell me how they tasted."

Yes, sir, said Fred, "I have, and they always taste very sweet."

That's quite true, Fred, replied Mr. Wilson. "Now, I have here some pea-meal. I will mix some of it into a paste with warm water, and you shall hold a little of the paste on your tongue."

Fred did as he was requested, and in a short time he was in possession of the whole secret.

I know what you wish me to find out, sir, he said. "The paste soon began to taste sweet. That proves that there is starch in the pea-meal. The saliva from my tongue turned the starch into sugar, and it is the sweetness of the sugar that I can taste."

Capital, said Mr. Wilson, "and now you know why the young green peas always taste sweet. Peas and beans of all kinds, like every other vegetable food, contain starch. They are less valuable, however, for the starch which they contain than for another constituent, of which we shall speak next. Indeed they contain less starch in proportion than any of the farinaceous foods of our recent lessons.

They all contain nearly a quarter of their weight (from 23 to 25 percent) of a valuable tissue-forming substance. That is, they contain much more tissue-forming matter than either wheaten flour, oatmeal, or butcher's meat. You remember I told you that the Latin name for pulse of all kinds is legumen. This name is now used by scientific men to describe, not the pulse itself, but the tissue-forming matter which it contains.

The legumin, when separated out from the starch and other matters of the seeds, is found to be very similar in character to the casein of cheese. In fact, the Chinese actually make a kind of cheese from the legumin of peas. Beans and peas, in the dried state, are not eaten very largely, in spite of their valuable tissue-forming legumin, for they are somewhat difficult to digest. Both, however, in their growing state as green vegetables, are favorites with most people, and are regarded generally as luxuries of the table.

The variety of beans, known as broad or great beans, are often used in their dried state for feeding horses. They are then commonly called horse-beans. We use the green pods as well as the seeds of the scarlet-runner and French bean, but the seeds only of the broad bean and pea are cooked.

When used in the dried state, the only things necessary to make peas and beans of all sorts excellent food are good soaking in cold water and careful cooking. A good plan is to soak them in cold water for one day, and then let them stand for a couple of days in their wet state. Under these conditions, the seeds will commence to grow, and as soon as this happens, the softened starch will be converted into sugar. They then require careful boiling for two or three hours. This treatment will render them perfectly digestible for all except the most delicate persons. It is in the highest degree important to remember that, provided they can be rendered easy of digestion, peas and beans are a most economical food, because they contain such a large proportion of the tissue-forming legumin.

One of the most valuable of these leguminous foods in the dried state is the haricot bean. This is in reality the dried seed of a small white variety of the French bean.