220 THE PRINCIPLES OP AGRICULTURE 



this ferment will coagulate 800,000 parts of 

 casein. 



393. In birds the gastric juice is secreted in 

 an enlargement of the gullet (proventriculus) 

 just above the gizzard. The strong muscles 

 and cartilaginous lining of the gizzard serve, 

 with the pebbles swallowed, to grind down the 

 food into a fine pulp and to mix it intimately 

 with the gastric juice. 



3d. Intestinal digestion 



394. Under the action of the saliva and gas- 

 tric juice, the greater part of the starch and ni- 

 trogenous matter is usually digested before the 

 food materials pass from the stomach into the 

 intestines. The products of digestion are mainly 

 sugar and peptones. The fatty matters, set free 

 by the digestion of their nitrogenous envelopes, 

 the undigestible portions, and such digestible 

 matters as are as yet not acted on, pass on into 

 the intestines, mostly in a finely divided semi- 

 fluid condition. 



395. In the intestines, the materials are acted 

 on by bile, pancreatic juice, and intestinal juice. 

 These fluids are alkaline. 



396. Bile is secreted by the liver. It is 

 poured into the intestines a few inches beyond the 

 stomach. It renders the contents alkaline, checks 

 fermentation, stimulates the movements of the 



