BIRDS. 



311 



the food is swallowed entire. When the food is flesh, the 

 process of digestion is sufficiently simple and rapid to need 

 no preparation; but in the case of the hard grains and 

 seeds that constitute the staple diet of so large a number 

 of species, a peculiar provision is requisite for grinding — a 

 sort of internal mill. 



This organ, well known as the gizzard, is endowed with 

 immense power for grinding and crushing; it is almost 

 wholly made up of two semi-globular masses of dense 

 muscle, the two opposing faces of which are coated with a 

 layer of thick leathery skin. Between these the vegetable 

 substances to be ground are dropped from the crop, just as 

 the corn is dropped from the hopper between the mill- 

 stones; and the force exerted when these faces work on 

 each other is immense, and all but irresistible. The faci- 

 lity with which substances the most hard, angular, and 

 even acute, are ground down, and that with perfect impu- 

 nity to the coats of the gizzard, is proved by the researches 

 of Plater, Reaumur, Redi, and Spallanzani. The experi- 

 ments of the last named philosopher possess the highest 

 interest : he introduced tin tubes variously strengthened 

 with wire, into the stomachs of Turkeys, and invariably 

 found them crushed, flattened, broken, and variously dis- 

 torted. Thick balls of glass were broken, ground down, 

 and in a few hours completely pulverised. Pieces of glass 

 w T ith sharp, jagged edges, shared the same fate, without in 

 the least wounding the callous skin of the gizzard. Needles 

 were cast into a ball of lead, so that their points projected 

 a quarter of an inch, and, being encased in a soft substance, 

 were thrust down the throat of a Turkey; in twenty-four 

 hours the points were broken off close or rubbed down, and 



