154 THE VITAL FUNCTIONS. 



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 instinct in the choice of the 

 proper materials for food, and for assisting its di- 

 gestion ; and if a mixture of a large quantity of 

 stones with a small proportion of grain be set be- 

 fore 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 sub- 

 stances may be derived from the experiments of 

 Spallanzani himself, who ascertained that grain is 

 not digested in the stomachs of birds, when it is 

 protected from the effects of trituration. 



Thus the gizzard may, as Hunter remarks, be 

 regarded as a pair of jaws, whose teeth are taken 

 in occasionally to assist in this internal mastication. 

 The lower part of the gizzard consists of a thin 

 muscular bag, of which the office is to digest the 

 food that has been thus triturated. 



Considerable differences are met with in the 

 structure of the gizzards of various kinds of birds, 

 corresponding to differences in the texture of their 

 natural food. In the Turkey, the two muscles which 

 compose the gizzard are of unequal strength, that 

 on the left side being considerably larger than that 

 on the right ; so that while the principal efibrt is 



