}22 ' THE PHILOSpPHY 



Thefe fadls, which our author candidly acknowledges had 

 been formerly oblerved, led him, id the year 1758, to make 

 experiments on the breathing of birds, in order to prove the 

 free communication between the lungs and the fcverai parts 

 of the body mentioned above. 



< Firft,' fays he, « I made an opening into the belly of a 



* cock, and having introduced a filver canula, tied up the 

 ^ trachea *, I found that the animal breathed by this opening, 



* and might have lived ; but, by an inflamation in the bow- 



< els coming on, adheiions were produced, and the commu° 

 ^ nication cut ofF. 



* I next cut the wing through the os humeri, in another 

 « fowl, and tjing up the trachea, as in the cock, found that 

 ^ the air pafTed to and from the lungs by the canal in this 



* bone. The fame experiment was made with the os femo- 



< ris of a young hawk, and was attended with nearly the like 



< fuccefs *.' 



The extreme fingularity of this almoil univerfal diffuiion 

 of air through the bodies of birds, naturally excited a delire 

 to difcover what might be the intention of Nature in pror 

 ducing a fi:ru£lure fo extraordinary. Mr. Hunter firft imagi- 

 ned that it might be intended to aflift the adt of flying, by 

 increaling the volume and ftrength of the animal, without 

 adding to its weight, which muft be diminifhed ; becaufe 

 the fpecific gravity of the external air is fuperior to that of 

 the internal air, which is rendered more rare by the heat of 

 the animal's body. This opinion was corroborated, by con- 

 lidering that the feathers of birds, and particularly thofe of 

 the wings, contain a great quantity of air. With his ufual 

 ingenuoufnefs, however, Mr. Hunter, in oppofition to his 

 fir ft conje(5lure, informs us, that the oftrich, which does not 

 fly, was amply provided with air-cells difperfed through its 

 body ; that the wood-cock, and fome other flying birds, were 

 * Ibid, page 8i. 



