BIRDS. 



SO? 



of the chest, admit the air freely into every part of the 

 interior : nay, more ; the atmospheric air bathes every 

 blood-vessel of any considerable size throughout the body, 

 passes into the hollow bones of the limbs, and even pene- 

 trates between the muscles, and into great membranous 

 cells beneath the skin.* V 



The consequence of tfylsoopious supply of oxygen to the 

 blood, not only in the lungs, but in every part of its course, 

 is a great increase of its heat, which far exceeds that of thef 

 most warm-blooded quadruped. The heat pervading the 

 whole of the animal tissues is communicated to the air, 

 which, as we have just seen, is so extensively distributed 

 about the body ; and thus the bird is not only rendered 

 light by being blown out with air, but that air is brought 

 up to a very high temperature, and so rarefied, and made 

 very buoyant. 



The animal heat thus generated must not be allowed to 

 escape too rapidly; and hence a body-clothing is provided, 

 which of all substances is perhaps the most effective non- 

 conductor of caloric. A feather is in itself a stud}^ When 

 we look at the whole covering of a bird, we cannot help 

 observing how soft, how light, how smooth, how compact, 

 how warm it is; and if we examine each feather separately, 

 there is not less to admire in the details of its structure. 

 It consists of two parts ; a light but firm shaft formed of a 



* This peculiarity was once brought strongly under our own observation in 

 the case of a pelican (Pelecanus fascus), which we were dissecting. The whole 

 inner surface of the skin on the trunk was cellular, especially on the breast, 

 forming an immense congeries of membranous bladders, inflated with air. As 

 an example of the free intercommunication that exists between the tissues of 

 the body, it may be mentioned that, in this specimen, the great gular poucb, 

 when filled with water (to the amount of seventeen pints), allowed it to escape 

 by di-ipping from a wound in the outer joint of the wing, 



