SOME ACCESSORIES 157 



through large channels to the air-sacs, and, when 

 expiration takes place, passes again, still almost 

 fresh, to the lungs, and some of it, getting from the 

 main passage to the little ramifications, continues the 

 process of oxidation. Thus, if the bird takes twenty 

 breaths in a minute, the lungs are supplied forty times 

 with fresh air. If he has hollow bones — and in some 

 birds almost all are hollow — pouches of pulmonary 

 membrane extend into the cavities, and thus the 

 bones are filled with air from the lungs (see p. 77). 



When a bird is standing his breastbone moves with 

 each breath ; in a captive bird this is easy to see. 

 In the case of Pelicans I have found the rate per 

 minute to vary from 5-11, from very slow to rather 

 slow, while in the most rapid breather, a Canary, 

 it was not far short of 100. Between these 

 extremes came a Blackbird with 39, a Bulbul with 

 48, an Ouzel with, at one time, 34, at another 50. 

 Evidently the big bird when at rest is a slow breather ; 

 a Griffon Vulture took only nine respirations. The 

 small birds are the more rapid, and as a rule they have 

 a higher temperature. The Great Tit and the Swift 

 are at one extreme with 111 2° F., and the Ostrich 

 at the other with 99'2°. In between come the Duck 

 with 109- 1° and the Heron with 1058°. The slow 

 breathing of the big birds during rest is remarkable, 

 but we cannot doubt that it becomes rapid during 

 flight, whether the bird be big or small. Unfortu- 

 nately it is very difficult to make observations, but 

 of the method of breathing we may get some idea 

 by watching a bird lying on his breast When he 

 adopts this attitude it is easy to see that his back 

 rises with each respiration, no movement being 



