366 
BIRDS. 
performs the rest ; frequently by the aid of little 
rugged stones, which the bird swallows in or- 
der to break the texture of the nutriment the better, 
and perhaps to keep the passages clear. Some cu- 
rious experiments, to prove the strength as well as 
the digestive powers of their stomachs, are to be 
found in the works of the abbe Spallanzani. 
The bones of birds, though of a solidity sufficient 
to sustain their bodies, are nevertheless so hollow 
and diminutive, that they scarce make any addition 
to the weight of their flesh. 
That which constitutes the pride and beauty of a 
bird, its plumage, is artfully formed and distributed, 
as well to sustain as to defend it from the injuries 
of the air. The quill of the feather is both firm 
and light ; and being at the same time hollow, it 
possesses a great deal of surface with little gravity, 
which places the bird almost in equilibrium with 
the air. The feathers are inverted behind, and laid 
one over another in a regular order. That part of 
them which is next the body is furnished with a 
warm and soft down ; and that next the air is ar- 
rayed with a double beard, in two ranks, and 
longer at one end than at the other. These beards 
are a row of little flat and thin plates or laminae, dis- 
posed and inserted in a line, as perfect as if their 
extremities had been cut with a pair of scissars. 
Each of these laminae is itself a quill or basis, which 
sustains two new ranks of a minuteness that almost 
renders them invisible, and which exactly closes up 
all the little intervals through which the air might 
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