72 MISCELLANEOUS 



their pastures, and their hunger begins when the 

 receiving stomach is empty, or nearly so. 



Birds which are exclusively vegetable in their 

 feeding, and those which are exclusively carnivo- 

 rous, may be regarded as the extremes of the class, in 

 so far as the alimentary system is concerned. The 

 former have that system largest, most complicated, 

 and most constantly in action, and the true stomach 

 always a gizzard. The latter have, in proportion 

 to the general size of their bodies, the alimentary 

 apparatus smallest, and also the most simple, — acting 

 readily, but acting, or recjuiring to act, only at inter- 

 vals; and they have the stomach always membranous. 



Those vegetable feeders that live much on seeds 

 and in temperate climates, which is the case with the 

 majority, require an auxiliary to even the muscular 

 action of the most powerful gizzard, in order so to 

 grind and divide the food as that the gastric juice 

 can act upon it. For this purpose they swallow small 

 stones and gravel ; and it has been observed that 

 some of the gallinaceous birds were kept in equal 

 condition and in better health upon much less food 

 when they had access to those auxiliaries. It is not 

 improbable that a small quantity of resisting matter 

 may help the digestion of all stomachs ; and that it is 

 upon this principle that brown bread is more diges- 

 tive by the human stomach than bread of the finest 

 flour, from which the whole of the husky matter is 

 separated. 



Intermediate between those two extreme forms of 

 the digestive system in birds, there are many mo- 

 difications, adapted to all varieties of food. Some 

 of them have the stomach more membranous toward 

 the one extremity, and more muscular toward the 

 other ; in some the character of the stomach is par- 



