164 
COMPENSATION. 
which is necessary, but which was before left imperfect. I 
say, the trituration which is necessary; for it appears from 
experiments, that the gastric fluid of sheep, for example, 
has no effect in digesting plants, unless they have been 
previously masticated; that it only produces a slight mac¬ 
eration, nearly as common water would do in a like degree 
of heat; but that when once vegetables are reduced to 
pieces by mastication, the fluid then exerts upon them its 
specific operation. Its first effect is to soften them, and to 
destroy their natural consistency; it then goes on to dis¬ 
solve them; not sparing even the toughest parts, such as 
the nerves of the leaves.* 
I think it very probable, that the gratification also of the 
animal is renewed and prolonged by this faculty. Sheep, 
deer, and oxen, appear to be in a state of enjoyment whilst 
they are chewing the cud. It is then, perhaps, that they 
best relish their food. 
II. In birds, the compensation is still more striking. 
They have no teeth at all. What have they then to make 
up for this severe want? I speak of granivorous and 
herbivorous birds; such as common fowls, turkeys, ducks, 
geese, pigeons, &.c. for it is concerning these alone that 
the question need be asked. All these are furnished with 
a peculiar and most powerful muscle called the gizzard; 
the inner coat of which is fitted up with rough plates, which, 
by a strong friction against one another, break and grind 
the hard aliment as effectually, and by the same mechani¬ 
cal action, as a coffee-mill would do. It has been proved 
by the most correct experiments, that the gastric juice 
of these birds will not operate upon the entire grain; not 
even when softened by water or macerated in the crop. 
Therefore, without a grinding machine within its body, 
without the trituration of the gizzard, a chicken would have 
starved upon a heap of corn. Yet why should a bill and a 
gizzard go together ? Why should a gizzard never be found 
where there are teeth? 
Nor does the gizzard belong to birds as such. A. giz¬ 
zard is not found in birds of prey. Their food requires 
not to be ground down in a mill.* The compensatory con¬ 
trivance goes no farther than the necessity. In both clas¬ 
ses of birds, however, the digestive organ within the body 
bears a strict and mechanical relation to the external in¬ 
struments for procuring food. The soft membranous sto¬ 
mach, accompanies the hooked, notched beak; the short 
Spall, dis. III. Sect. 140. 
