406 THE FEEDING OF ANIMALS 



products of metabolism, that an accurate estimation of 

 the digestibility of food by birds is so difficult. No satis- 

 factorily acciu-ate methods for separating some of the 

 nitrogenous residues from different organs seem yet to 

 be perfected. 



Into the intestine shortly after it leaves the gizzard 

 two ducts from the liver and two from the pancreas enter, 

 discharging the bile and pancreatic juices. The liver, as 

 usual, is a large organ. The pancreas also is very largely 

 developed, and extends for several inches along the duo- 

 denal loop of the intestines, reaching in the common 

 fowl a length of over 5 inches. 



Altogether the structxU-e of the digestive ajqjaratus of 

 birds indicates extreme efficiency and the capacity for 

 rapid work. A study of it suggests, also, as does that of 

 any complicated and delicately adjusted apparatus, that 

 it should not be overloaded nor violently distiu"bed when 

 running at high pressure. It may be said to rim at high 

 pressure while the extremely rapid growth of yoimg 

 birds occurs and during the extended laying season, for 

 the resulting products call for an uninterrupted supply 

 of food and the transformation of all material that is 

 available. Chickens of two pounds weight at ten weeks 

 of age show a igain over the weight of the first week of 

 nearly 1,700 per cent. Ducklings five pounds in weight 

 at nine weeks show a gain during about eight weeks of 

 3,900 per cent. Such rates of growth are not very unusual 

 for young fowls under favorable conditions. 



494. Constituents of the body of the hen. — ^Whether 



the production of meat or of eggs is the prime object, 



the young fowl must first be grown. It is desirtible, lien, 



, to consider what constituents make up the body of the 



animal, for all must be derived from the food. Many 



