444 
RESPIRATION AND EXCRETION 
Student Report on Respiration 
Get Oxygen 
Get Rid of Car¬ 
bon Dioxide 
Breathe Through 
Water 
Air 
Water 
Air 
Skin 
Gill 
Lung 
Air 
Tubes 
Leaves 
Amoeba 
Crayfish 
Fly 
Clam 
Toad 
Bird 
Man 
Bean 
Yeast 
Organs of Respiration in Man. -— Air enters the nose and 
passes into the windpipe or trachea (tra'ke-a). The opening 
into the windpipe is covered by the epiglottis (Greek, epi, 
upon; glotta, tongue), which is raised during breathing and 
closed when food is swallowed. The windpipe divides into 
two branches, one entering each lung. Each branch is called 
a bronchus. The windpipe and bronchi are the air passages 
which carry air to the lungs. These passages are kept open 
by numerous stiff cartilage rings, which, in the trachea, are 
not entirely complete on the side of the esophagus, and in the 
smaller tubes even less so. 
On entering the lung each bronchus divides into branches 
which in turn branch out again and again, until the entire 
lung is penetrated in all its parts by these passages. Finally 
each branch ends in a small pouchlike sac called an air cell. 
The walls of the air cells are thin, and the cells themselves 
are surrounded by minute branches of the blood vessels. 
It is estimated that the highly folded condition of the walls 
of the bronchi make a surface larger than the entire surface 
of the body. All these thin walls of the lungs and blood 
