12 Ornithology. 



air with astonishing rapidity.^ The structure of insects is not 

 a little analogous. 



The almost universal diffusion of air in the bodies of birds 

 is of infinite use to them, not only in these long and laborious 

 flights, but likewise m preventing their respiration from being 

 stopped or interrupted by the rapidity of their motion through 

 a resisting medium. Were it possible for man to move with 

 the swiftness of a swallow, the actual resistance of the air, as 

 he is not provided with internal reservoirs similar to those of 

 birds, would soon suffocate him. 



Stomach of Birds. The stomach of birds forms them 

 into two distinct natural classes; those with cartilaginous 

 stomachs, covered with very strong muscles, called a gizzard ; 

 and those with membranous stomachs more resembling that 

 of carnivorous quadrupeds. The former is given to birds 

 whose principal food is grain and seeds of various kinds, or 

 other hard substances that require much friction to communi- 

 cate, to assist which, gravel is necessary ; the latter is given 

 to birds which feed upon flesh or fish, and whose digestion is 

 accelerated more by the gastric juice than by the action of 

 the stomach. Those of the first class digest or retain every 

 substance swallowed ; and those which eject or disgorge 

 innutritions matter unavoidably taken in, such as feathers, fur, 

 bones, &,c. belong to the second class, as is conspicuous in 

 the falcon, owl and others that feed on fish. Granivorous 

 birds seem to possess the power of retaining the small stones 

 taken into the gizzard, or evacuating them, when they become 

 polished and less useful, but cannot disgorge them. In a 

 state of nature the quantity of gravel taken in must be regu- 

 lated, no doubt, by the sensation of the stomach ; but, won- 

 derful as it may seem, in domesticated animals those instinc- 

 tive faculties are deranged. Instances frequently occur 

 where the whole cavity of the gizzard is filled with gravel 

 stones. The food of granivorous birds is conveyed entire 

 _^,into the first stomach, or craw, where it undergoes a partial 

 •<^" dilution by a liquor secreted from the glands, and spread 

 [Over its surface. It is then received into another species of 



* Humboldt saw the enormous vulture of the Andes, the majestic con- 

 dor, dart suddenly from the bottom of the deepest valleys to a considera- 

 ble height above the summits of Chimboraco, where the barometer must 

 have been lower than ten inches. He frequently observed it soaring at 

 an elevation six times higher than that of the clouds in our atmosphere. 

 This bird, which reaches the measure of fourteen feet with the wings ex- 

 tended, habitually prefers an elevation at which the mercury of the ba- 

 rometer hiifika to about sizteeo ioches. 



