184 ANIMAL ACTIVITIES. 
The adult frog pumps the air into the lungs by the 
movements of the muscles of the throat and lower part 
of the mouth-cavity. When the mouth-cavity enlarges, 
air rushes in through the nostrils. When the cavity 
contracts, valves close the openings to the nostrils and 
the air is forced down into the lungs. The frog has 
Fic. 140.—Blood-corpuscles of Man. 5s, 7’, 7’, red corpuscles; ~ and 
&, white corpuscles; ¢, crystals. 
neither ribs nor diaphragm—organs of great importance 
in our own breathing. 
The oxygen, once taken by the blood, is carried by 
the red corpuscles, or blood-cells, to all parts of the 
body, where in the capillaries it is given up to burn, 
or oxidize, tissues and food substances in order to 
produce heat and energy. 
Nutrition. Food passes from the mouth to the 
stomach, where it is acted on by fluids like those in our 
own bodies. It then passes to the intestines, where 
the bile secreted by the large liver and the pancreatic 
