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 arule 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 105°8°. 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 
