122 ANIMAL LIFE 



control governs its uniformity, and there results a 

 higher temperature than any we can healthily evolve, 

 and one that for the first time in our resume of living 

 beings is unaffected by that of its surroundings. A 

 hen's temperature is uniformly 103 degrees Fahrenheit ; 

 a swallow's, 106 degrees. 



The production of voice is partly voluntary, partly 

 mechanical. The adjustment of the slit just above 

 the lungs and the rate of vibrating its edges are modi- 

 fiable muscular actions. The call note, the migration 

 note, the mating song, the alarm note, and the mimicry 

 of parrots and song-birds are controllable responses 

 to an impulse or an audible voice. But the ordinary 

 breathing movement, which underlies it all, has become 

 part of that unreasoning mechanism over whose 

 starting or finishing birds have no voluntary control. 

 The combination of superb singing powers with high 

 vitality and spacious breathing marks the bird. 



In the mammals the lungs are capacious ; but the 

 amount of really tidal air is a mere fraction of the 

 whole, and forms a top layer, from which the great 

 mass that is stationary gains its oxygen, and into 

 which it diffuses its carbonic acid. Thus, between 

 the lungs and the tidal air is a diffusion-chamber. 

 Every beast and child fills this with its first breath 

 and never breathes as deeply again. 



Movements of the lungs are those of enlargement 

 and diminution. Both of these are effected by the 

 chest and by the diaphragm, a device peculiar to 

 mammals. Both take place through the nose, as in all 



