Organs of Nutrition Li7 
surely return to outdoor study of the daily life of these 
creatures, with more balanced interest, and a “little 
knowledge” which, instead of being a ‘‘dangerous thing,” 
will, in this instance, add many fold to our appreciation 
d 
of the external results of these functions, whose work- 
ings are ever concealed from the light of day. 
The digestive apparatus of a bird, or indeed of any 
creature with a back-bone, is in reality a tube or canal, 
which begins at the mouth and extends through the 
body. Certain portions are contracted or expanded, and 
specialized to store up, moisten, grind, dissolve, digest, or 
absorb the food substances which pass through. 
The Salivary Glands 
The mucous membrane, or lining, of the entire diges- 
tive canal is very delicate and requires to be kept con- 
stantly moist. The lining of the mouth and throat, being 
so exposed to contact with the outer air, requires some 
special provision to lubricate it. This is accomplished 
by certain glands, some beneath the tongue, others situ- 
ated in the upper portion of the mouth. These are not 
found in fishes, nor in other creatures which live alto- 
gether in the water; but in reptiles several groups are 
distinguishable. In birds they vary greatly, some having 
scarcely a trace, while others have large well-developed 
glands. Salivary is the common name given to certain 
of these, and we will let that name represent all. 
In ourselves, saliva is an important aid in digestion. 
Besides moistening the food and softening all hard por- 
tions, it exerts active chemical effects, as, for example, 
