CAGE BIRDS AND THEIR DISEASES, 415 
depend the health of the body. Two peculiarities in the anatomy and 
physiology of birds need special mention here, as bearing directly upon the 
topic now before us. First, the lungs are very small, but the bones are pro- 
vided with various air-cells which may be filled or emptied at will to regu- 
late the buoyancy needed for flying. If the food is of such a natine as to 
interfere with this function, it is evident that the general health will be 
disturbed and the facility of flight be impaired. Second, the digestive or- 
gans exhibit differences according to the various kinds of food which the 
Creator designed for them. In song-birds, for example, there are three 
successive cartilaginous stomachs, covered with strong muscles.. Indeed, 
ary. CANARIES 4ND NEST. 
organs. of this kind are given to all birds which live on grains, seeds and 
other hard food, and the requisite grinding is effected by small stones taken 
into the gizzard. This also emphasizes the necessity of giving to every 
bird the kind of food which it would get in a state of nature. 
[t is manifest that the only rational principle for adoption in feeding is 
to accord to a bird a diet as nearly identical as possible with what nature 
has especially provided for it. Since this natural method cannot le used 
for birds in confinement in all its details, onc must meet the lack of nature’s 
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