INTRODUCTION. 7 S 



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. 



The digestive organs of birds form 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 those of carnivorous 

 quadrupeds. The former is given to birds, the principal food 

 of which is grain and seeds of various kinds, or other hard sub- 

 stances that require much friction to divide, or comminute, to 

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

 which feed upon flesh or fish, and whose digestion is accele- 

 rated more by the gastric juice than by the action of the 

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

 stance swallowed; and those which eject or disgorge innu- 

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

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

 those that feed on fish. Graminivorous 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 regulated, no doubt, by the 

 sensation of the stomach ; but, wonderful as it may seem, in 

 domesticated animals, those instinctive faculties are deranged. 

 Instances frequently occur where the whole cavity of the 

 gizzard is filled with gravel stones. The food of graminivorous 

 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 stomach, where it is still further diluted, 

 after which it is transmitted into the gizzard, or true stomach, 

 consisting of two very strong muscles, externally covered with 

 a tendinous substance, and lined with a thick membrane of 

 prodigious power and strength, in which organ the food is com- 

 pletely triturated, and prepared for the operation of the gastric 

 juices. 

 i Graminivorous birds partake much of the nature and dispo- 



