英文科學(xué)讀本 第三冊(cè)·Lesson 33 A Fish

Lesson 33 A Fish

You know, Norah, said Fred, "that a man, a dog, or a rabbit would die if held under water, and that a fish dies as soon as it is taken out of the water. But don't you think it is very strange that both die from the same cause? They both suffocate. One cannot breathe in the water, the other cannot breathe out of it. Teacher has been helping us to understand how a fish can live and breathe in the water."

He had a fresh herring for the lesson, and as mother has bought some for supper, I asked her to let me have one to show you.

Here it is. Now look at these long slits, just behind the jaws. Lift up one of them, and inside you will see the red gills. The gills are the lungs of the fish, for fishes have no lungs such as we have. Fishes cannot live without breathing air any more than we can. We breathe by means of lungs, the fish by means of gills.

But I can't see how a fish can breathe air, said Norah, "while it is living and moving about in the water."

Ah, said Fred, "that is the wonderful part of it. You remember that water is porous, and that it absorbs air. Water, in fact, always contains air. The fish lives by robbing the water of some of the air, which it breathes in through its gills."

If you notice a fish swimming in the water, you will see that it is constantly opening and shutting its mouth, as if it were drinking. It is not drinking. It takes the water into its mouth, but only to pass it backwards over the gills, and so out again through the slits at the sides.

Teacher explained what all this means. He pointed out the redness of the gills, and he told us that, if our eyes were sharp enough, we should find these gills crowded with tiny blood-vessels. It is the blood in these vessels which gives the gills their red color.

Every time the fish takes in water through its mouth, and pours it over the gills, the blood in the little vessels sucks up as much of the air as it can get from the water.

This is the creature's way of breathing.

SUMMARY

The fish breathes by means of gills. The gills are placed just behind the jaws. They look red, because of the blood which is flowing through them. The fish takes in water at its mouth, and passes it over the gills. The water contains air in its pores. The gills suck this air out of the water.