INTRODUCTION. 
7 
the swiftness of a swallow, the actual resistance of the air as 
he k not provided with internal reservoirs similar to those of 
birds, would soon suffocate him 
The digestive organs of birds ibrm them into two distinct 
natural classes; those with cartilaginous stomachs, covereu 
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 fram 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 mu^les, 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. 
Graminivorous birds partake much of the nature and disp 
