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 an}' 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" — 

 factors 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. 



