172 THE VITAL FUNCTIONS. 



merely by accident, or in consequence of the 

 stupidity of the bird, which mistakes them for 

 grain. But this opinion has been fully and 

 satisfactorily refuted both by Fordyce and by 

 Hunter, whose observations concur in establishing 

 the truth of the common opinion, that in all 

 birds possessing gizzards, the presence of these 

 stones is essential to perfect digestion. A greater 

 or less number of them is contained in every 

 gizzard, when the bird has been able to meet 

 with the requisite supply, and they are never 

 swallowed but along with the food. Several 

 hundred were found in the gizzard of a turkey ; 

 and two thousand in that of a goose: so great 

 an accumulation could never have been the 

 result of mere accident. If the alleged mistake 

 could ever occur, we should expect it to take 

 place to the greatest extent in those birds which 

 are starving for want of food ; but this is far 

 from being the case. It is found that even 

 chickens, which have been hatched by artificial 

 heat, and which could never have been instructed 

 by the parent, are yet guided by a natural in- 

 stinct in the choice of the proper materials for 

 food, and for assisting its digestion : and if a 

 mixture of a large quantity of stones with a 

 small proportion of grain be set before them, 

 they will at once pick out the grain, and swallow 

 along with it only the proper proportion of stones. 

 The best proof of the utility of these substances 



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