THE NUTRIENTS AND NUTRITION 311 



Fat soluble A is found in abundance in tlie fresli i,'reen 

 leaves of plants and in butter fat. Its lack in a ration brings 

 on a general unthrift and in i)articular a characteristic 

 pathological condition of the eyes. 



Both vitanuns are more or less easily destroyed, the water 

 soluble being more sensitive to adverse conditions than the 

 fat soluble. The drying of the legumes to make hay reduces 

 their vitamin content and may totally destroy it. Heating 

 to high temperatures is also likely to destroy or at least reduce 

 the amounts of these substances. 



DIGESTION. 



Definition of Digestion. — Digestion is the process, accom- 

 plished by the crop, glandular stomach, gizzard, pancreas, 

 liver, and intestine, of so dissolving and chemically changing 

 the material taken into the alimentary tract that it can be 

 absorljed l)y the l)lood and used by the body. 



The Digestive Tract. — "The structure of the alimentary 

 canal of the bird suggests that the digestive process is rapid 

 and that it partakes of features associated with both the 

 carnivora and herbivora. Thus the relative shortness in 

 length is a carnivorous characteristic, while the character 

 of the diet and the thorough comminution of the food in the 

 gizzard are features more akin to the herbivorous type."' 



Mouth Parts} — The distinctive character of the mouth 

 of birds is the absence of lips and teeth, these parts being 

 replaced by a horny mandible on each jaw and forming the 

 beak of the land fowl and the bill of the water fowl. With 

 land fowl the beak is short, pointed, thick and strong, the 

 upper mandible curving over the lower. In w'ater fowl the 

 bill is longer, less firm, flatter, widened at its outer end, and 

 supplied along the edges of each mandible and within the 

 mouth with a series of thin and sharp transverse laminte, 

 whose purpose is to cut soft herbage. 



' Brown, Bureau of Animal Industry, Bulletin No. 56. 



2 This account of the digestive tract is gleaned from various sources, 

 principally McNair, New York State Veterinary College Laboratory 

 Bulletin No. 3, Chaveauxs' Comparative Anatomy of Domestic;* ted 

 Animals, and F. Smith's Manual of Veterinary Physiologj'. 



