118 The Bird 
changing starch to sugar and in many other ways making 
ready the food, that the important changes which take 
place in the stomach may begin at once. In birds, how- 
ever, the saliva has but little chemical effect on the food, 
its principal use being to moisten the substances before 
they are swallowed. 
It is not often that Nature, when she has produced 
Fie. 90 —Nest of Chimney Swift; twigs glued together with saliva. 
an organ or special tissue by the elaborate synthesis of 
evolution, confines its use to any one function. If birds 
were provided with salivary glands intended only for the 
purpose mentioned above, they soon found other uses for 
them. In a woodpecker we will find very large salivary 
glands on each side of the mouth. These secrete a sticky 
liquid which covers the long, many-barbed tongue and is 
an efficient aid in picking out insects from their holes in 
the bark and wood of trees. 
