There are two reasons then why we breathe: (_a_) to obtain oxygen; (_b_) to get rid of carbonic-acid gas.
~11.

How a Frog Breathes.~--Did you ever see a frog breathe?
If not, improve the first opportunity to do so.

You will see that the frog has a very curious way of breathing.

He comes to the top of the water, puts his nose out a little, and then drinks the air.

You can watch his throat and see him swallowing the air, a mouthful at a time, just as you would drink water.
~12.~ If you had a chance to see the inside of a frog you would find there a queer-shaped bag.