英文科學(xué)讀本 第六冊(cè)·Lesson 13 Animals Useful for Food

Lesson 13 Animals Useful for Food

In dealing with the vegetable food-stuffs we took bread in some form to be man's staple food. We commenced our investigation of these vegetable foods by examining the composition of wheaten bread, and we found that every kind of bread must contain similar materials, and possess similar nutritive properties.

We shall now follow the same plan in dealing with flesh foods, taking a piece of lean beef for our first investigation. If we get a piece of newly-cut lean beef, fresh from the butcher, we find that it is moist. This is due to the water which the flesh contains. We must get rid of this water before we can learn anything about the composition of the beef. The best plan is to let it dry slowly on a tin plate in the hot sun. The water will evaporate gradually, leaving the meat dry.

As the drying goes on the beef shrinks considerably in size. In fact, if the original piece weighed a pound, we should have, after the drying, less than a quarter of a pound of perfectly dry flesh. That is to say, three-quarters of its weight is water.

We can find out by experiment what are the constituents of the dry flesh. A piece of fresh beef has a red appearance, owing to the blood which it contains. We can easily get rid of the blood by repeatedly washing the flesh in fresh water, and it will then be seen to consist of a mass of whitish fibers or threads, with little particles of fat interspersed among the fibers.

If this be put into spirits of wine, the fat will all dissolve out of it, and nothing will remain but the fibrous tissue, which is the principal solid constituent of the muscles, or lean flesh, of animals. It is known in the scientific world as myosin.

When we eat meat it is this part of it—myosin—that becomes tissue-forming food. It is the nutritive part of flesh food, as gluten is of vegetable food. In fact, myosin of flesh and gluten of the vegetable may be considered as identical in this respect.

Lean meat, however, contains nearly three times as much flesh-forming material as bread. It contains no starch, while bread has half its entire weight of this material.

Civilised man in all parts of the world has always reared and kept certain animals for food. To distinguish these from the wild animals of the chase, we speak of them as domesticated animals. The chief of them are the ox, the sheep, and the pig. The cow not only provides us with flesh food when dead, but also while living gives milk. Milk is in itself a valuable food; we use it in its simple form, and we convert it into butter and cheese.

The flesh of the sheep is eaten only as fresh mutton; the pig's flesh is not only eaten fresh, but it is salted, smoked, and cured into bacon and hams.

Poultry, eggs, and game form important items in our animal food. In addition to Englands home-supply they import poultry very largely from other countries, especially from France. In 1886 England spent on eggs alone ￡2,879,000, most of the eggs coming from France.

Fish of various kinds must be reckoned among the important articles of the food-supply; the fisheries of Great Britain are a source of great wealth to the country. The cod, herring, mackerel, salmon, haddock, and pilchard are among the most valuable catches, and oyster cultivation is prosecuted on various parts of the coast. The herring fishery is carried on chiefly round the Scotch coasts; the pilchard fishery is confined to the southwestern corner of the island.

In 1887 it was estimated that 125,000 men and 32,000 boats were actively engaged in the British fisheries. The most valuable of the British fishing-grounds is the Dogger Bank, between England and Holland.

Among the most important and productive fisheries of the world are those of Newfoundland, Nova Scotia, and New Brunswick. Cod is the chief fish caught, but the Gulf of St. Lawrence absolutely teems with fish of almost every variety.

The annual value of these Canadian fisheries varies from four to six millions sterling.