OF NATURAL HISTORY. 2$B 



^ we may rcafonably conclude they are, birds have an ad- 



* vantage over animals having teeth, fo far as flones are 

 « always to be found, while the teeth are not renewed. If we 



* conftantly find in an organ fubftanccs which can only be 



< fubfervient to the fun6lions of that organ, fliould we deny 



< them that ufe^ although the part can do its office without 



< them ? The ftones affiil: in grinding down the grain, and, 

 « by feparating its parts, allow the gaflric juice to come more 



< readily in contafl with it.' 



The next feries of experiments were made upon animals 

 with what Spalanzani denominates intermediate ftomachs be- 

 tween the mufcular and membranous, as ravens, crows, herons, 

 &c. The povver and a£lion of thefe intermediate ftomachs are 

 fuperior to thole of the membranous kind, but greatly inferior 

 to thofe of the m.ufcular. The tin tubes, or balls, which 

 pigeons and turkeys, foon flatten and disfigure, remain unal- 

 tered in the ftomach of crows. Their gaftric m.ufcles, how- 

 ever, are by no means inert. Though they are unable to 

 comprefs or diftort tin tubes, they are capable of producing 

 this effect upon thin tubes of lead. Birds whofe ftomachs 

 are of an intermediate kind, vv^ith regard to the thicknefs 

 and ftrength of their mufcular coats, may be denominated 

 onmivoroiis. They eat grafs, herbs, grain, and flefh of every 

 kind. When we make experiments, upon the digeftivc 

 powers of gallinaceous birds, the animals muft be killed be* 

 fore we can learn what effe£l:s have been produced on the' 

 fubftances inclofed in the balls or tubes. But, on crows 

 and ravens, experiments of this kind may be repeated as- 

 often as v/e pleafe, without deftroying a fingle individual. 

 £ubftances which they are incapable of digefting, as metal- 

 He tubes, they have the power of difgorging, or returning 

 by the mouth, in the fame manner as falcons, and other birds 

 of prey, throw up the feathers and hair of the animals they 

 have devoured. In birds of prey, this vomiting is common-* 



