50 THE STOMACH. 



namely, the different force with which it acts on the 

 various substances used for food by different birds. 

 Thus the gastric juice in the stomach of those birds 

 which live on flesh acts very sparingly on vegetable sub- 

 stances. On examining the castings or pellets of some 

 Eagles, which had been occasionally fed with dead Pigeons, 

 it was found, that the vegetable food, peas, wheat, and 

 barley, which had been swallowed by these birds of prey, 

 enclosed within the crops of the Pigeons, remained entire, 

 being only somewhat enlarged by heat and moisture; 

 though the fleshly substances, even to the very bones, 

 were entirely consumed*. 



Again, it has been observed, that this juice will not 

 act upon the grain swallowed by poultry, and other 

 granivorous birds, while it remains whole and entire. 



This fact has been further proved by actual experi- 

 ment. Some gastric juice was poured into a cup con- 

 taining some whole seeds, but it produced no effect upon 

 them till they were crushed. Hence it has been found, 

 that if oats and barley given to horses are previously 

 killed by heating, and crushed, the animal only requires 

 half the quantity, and yet thrives equally well. 



In considering the real stomach or gizzard, by which 

 name it will be more familiarly known, we shall find 

 additional cause for admiration, in the mode by which 

 Providence, with reference to the food introduced, so 

 nicely balances the grinding powers of the gizzard with 

 the dissolving or melting powers of the gastric juice. 

 This third or real stomach differs, like the gullet, crop, 

 and second stomach, very materially in different birds; 

 but, generally speaking, the action of this gizzard may 

 be compared to that of a coffee-mill, grinding down the 

 various substances introduced, into a pulpy matter. In 

 those which feed on flesh and insects, substances of no 

 very hard texture, this stomach appears as a thin mem- 

 branous bag, in comparison with the thick muscular 

 globes or gizzards of the grain-devouring class; and the 



* Zoological Journal, vol. x, p. 186. 



