INTRODUCTION. 
3 
quickly bring on suffocation. The superior vital heat of this class 
of beings is likewise^ probably due to this greater aeration of the 
vital fluid. 
Birds, as well as quadrupeds, may be generally distinguished 
into two great classes from the food on which they are destined 
to subsist ; and may, consequently, be termed carnivorous and 
granivorous. Some also hold a middle nature, or partake of both. 
The granivorous and herbivorous birds are provided with larger 
and longer intestines than those of the carnivorous kinds. Their 
food, consisting chiefly of grain of various sorts, is conveyed whole 
into the craw or first stomach, where it is softened and acted upon 
by a peculiar glandular secretion thrown out upon its surface ; 
it is then again conveyed into a second preparatory digestive 
organ ; and finally transmitted into the true stomach or gizzard, 
formed of two strong muscles, connected externally with a tendinous 
substance, and lined internally with a thick membrane of great 
power and strength ; and in this place the unmasticated food is at 
length completely triturated, and prepared for the operation of the 
gastric juice. The extraordinary powers of the gizzard in commi- 
nuting food, to prepare it for digestion, almost exceeds the bounds 
of credibility. Turkeys and. common fowls have been made to 
swallow sharp angular fragments of glass, metallic tubes, and balls 
armed with needles, and even lancets, which were found broken 
and compressed without any apparent pain to the subjects, or 
wounds in the stomach. The gravel pebbles swallowed by this class 
of birds with so much avidity, thus appear useful in bruising and 
comminuting the grain they feed on, and preparing it for the solvent 
action of the digestive organs. 
Those birds which live chiefly on grain and vegetable substances, 
partake in a degree of the nature and disposition of herbivorous quad- 
rupeds. In both, the food and the provision for its digestion, are very 
similar. Alike distinguished for sedentary habits and gentleness 
of manners, their lives are harmlessly and usefully passed in col- 
lecting seeds and fruits, and ridding the earth of noxious and 
destructive insects ; they live wholly on the defensive with all the 
feathered race, and are content to rear and defend their offspring 
from the attacks of their enemies. It is from this tractable and 
gentle race, as well as from the amphibious or aquatic tribes, that 
man has long succeeded in obtaining useful and domestic species, 
which, from their prolificacy and hardihood, afford a vast supply of 
wholesome and nutritious food. Of these, the Hen, originally from 
