The frog has no ribs; he does not breathe as we do. He shuts his mouth, sucks the air up through his nostrils, and swallows it in gulps. The frog can breathe through his moist skin. He spends all the winter in the mud at the bottom of the pond. His blood is always cold.
Lesson 28
More about the Air
"You remember our talk about the water bottle and the basin of water, Norah?" asked Fred. "What did we learn from it?""We learned that air is an actual substance, and that it takes up space although we cannot see it. The bottle was full of air, and that was why the water would not go in. When you slanted the bottle the air bubbled out, and the water went in.""That"s very good," said Fred, "and you must remember that there is air everywhere-in every nook and corner. Whatwe call "empty" is really "full of air."
"Teacher showed us a machine called an air- pump today. It will removethe air from a vessel and make it really "empty." He showed us too an "empty" square box, a foot across each way, and of course it was full of air. He said that if he could pump all that air out, the box wouldweigh just an ounce less than it did at first. Can youtell me what that proves?"
