292 NATURAL THEOLOGY. 



mechanical operation of the stomach as we have 

 described in the gizzard, fitted the food to supply 

 the nourishment of the body : but, we repeat, 

 that it has no further operation than that of com- 

 minuting the hard food, and preparing it for the 

 action of this animal fluid, the gastric juice, which 

 digests ; and digestion is the first process of assi- 

 milation. 



It may be interesting to the reader to know 

 that the lower orifice of the gizzard, where it 

 opens into the first intestine, {duodenum^ is dif- 

 ferently guarded in different families of birds. In 

 birds which have abundance of food, the gizzard 

 has no valve to retard its escape ; so that a 

 greater part of the grains or seeds on which they 

 feed passes off undigested ; a fact which we 

 touched upon elsewhere. Were birds of prey 

 furnished with the same grinding apparatus which 

 is suited for birds that feed upon grain, our argu- 

 ment would be overturned. But in them the 

 gizzard is very weak ; the cuticular lining of the 

 stomach very thin ; and the gastric glands, which 

 pour out the digesting fluid, very large. In the 

 hawk and kite we find no such macerating crop 

 as in the domestic fowl. 



Our author states that one class of birds can- 

 not digest grains ; the other cannot digest flesh. 

 This, however, taken literally, does not accord 

 with the experiments of Mr. Hunter, since he 

 brougiit the carnivorous birds to live on grains, 

 and the granivorous fowls to live on meat. But 



