38 
SECOND BOOK. 
“ I cannot understand how any creature can find 
air in the water,” said Arthur. 
4 . “Well, let me explain,” said Mr. Johnson. 
“ You know that water will dissolve sugar and salt, 
so that, although they are in it, they cannot be seen. 
So, too, water can dissolve the oxygen gas which 
animals need to keep their blood pure. 
5. “ Oxygen can get into the blood either in the 
gills or in the lungs; but 
the gills are made for tak- 
ing it only from the water, 
and the lungs for taking 
it from the air. That is 
why not only fishes, but 
also amphibians in their 
first stage of life, having 
gills, can live entirely 
under water, and why animals with lungs cannot.” 
6. The boys listened to Mr. Johnson’s explanation, 
and seemed to understand it. Then they asked their 
friend if he had any other amphibians to show them. 
7. “Here is a large bull -frog,” he continued. 
“ When alive it was not satisfied with snails and 
insects, but would eat a small bird if it had the 
chance. And here is a pretty little tree-frog, with 
very peculiar feet. They are fitted with suckers, 
by which the little creature holds on to the tree. 
“ Of course you observe that the fully-developed 
frogs and toads are without tails; the salamanders, 
Bull-frog. 
