The Breath of a Bird 177 
but entirely through the lungs into the air-sacs, giving, 
therefore, the very best chance for oxygenation to take 
place in every portion of the lungs. When we compare 
the estimated number of breaths which birds and men 
take in a minute—thirteen to sixteen in the latter, twenty 
to sixty in birds—we realize better how birds can per- 
form such wonderful feats of song and flight. 
Birds, having no sweat-glands in the skin, and the 
action of the capillaries being impeded by the feathers, 
would have no way of regulating the temperature of the 
body, much as this is necessary in flight, if it were not 
that the great quantity of air exhaled with each breath 
relieves the body of any excess of heat. 
However directly or indirectly the air-sacs are con- 
cerned with flight, a bird which sings uninterruptedly 
as it flies upward must be immeasurably aided by the 
great quantity of air at its command. And again, when 
a Prairie Hen inflates the orange-hued air-sacs on both 
sides of its neck, there is only one explanation as to 
their use, at least at the time of courtship, namely, an 
added decoration, and as an aid in the ‘“booming’’— 
tactors both of which, for aught we know, may help to 
soften the hearts of the coquettish females. 
Looking down the scale of life we find an animal among 
the reptiles with a lung which at once suggests that of 
a bird. The lungs of a chameleon are spongy and com- 
pact in front, but farther back they are hollow, and 
give off a dozen or more finger-like tubes or lobes, thus 
foreshadowing, at least in appearance, the air-sacs 
of birds. 
