INTRODUCTION. ix. 



to this, he informs us that the Ostrich, which does not fly, 

 is nevertheless provided with air-cells dispersed through its 

 body; that the Woodcock, and some other flying birds, are 

 not so liberally supplied with these cells; yet, he elsewhere 

 observes, that it may be laid down as a general rule, that in 

 birds who are enabled to take the highest and longest flights, 

 as the Eagle, this extension or diffusion of air is carried fur- 

 ther than in others; and, with regard to the Ostrich, though 

 it is deprived of the power of flying, it runs with amazing 

 rapidity, and consequently requires similar resources of air. 

 It seems therefore to be proved, evidently, that this general 

 diffusion of air through the bodies of birds is of infinite use 

 to them, not only in their long and laborious flights, but 

 likewise in preventing their respiration from being stopped 

 or interrupted by the rapidity of their motion through a re- 

 sisting 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.* 



Birds may be distinguished, like quadrupeds, into two 

 kinds or classes granivorous and carnivorous; like quadru- 

 peds too, there are some that hold a middle nature, and par- 

 take of both. Granivorous birds are furnished with larger 

 intestines, and proportionally longer, than those of the car- 

 nivorous kind. Their food, which consists of grain of 

 various sorts, is conveyed whole and 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 further diluted; after which it is transmitted into the 



* May not this universal diffusion of air through the bodies of 

 birds, account for the superior heat of this class of animals ? The 

 separation of oxygen from respirable air, and its mixture with the 

 blood by means of the lungs, is supposed, by the ingenious Dr. 

 Crawford, to be the efficient cause of animal heat. 

 VOL. I. b 



