98 PRINCIPLES OF VETERINAEY SCIENCE 



by the horse per hour. The principal constituents are water 

 about 92 per cent., the salts of the bile acids, biliary pigments, 

 and the waste products lecithin and cholesterol. 



The salts of the bile acids are sodium glycocholate and tauro- 

 cholate. The former is found in larger quantities in herbivora. 

 These salts precipitate proteins of the ingesta thus delaying 

 their passage and giving the digestive juices more time to act. 

 They prepare fats for emulsification and favor their absorption. 



The bile-pigments are bilirubin and jbiliverdin. The first 

 is apparently derived from the blood-pigment. Biliverdin is 

 produced from bilirubin by oxidation, and gives the bile its 

 characteristic color. 



Although bile acts on proteins in a limited way, its chief func- 

 tions are to dissolve and emulsify fats. It is most active in the 

 presence of pancreatic juice. However, bile is so unimportant 

 that intestinal digestion can proceed without its presence. 



Pancreatic juice reaches the intestine of the horse by two 

 separate and distinct ducts, as already described. The ox has 

 but one duct for this product. The secretion is indirectly stimu- 

 lated to production by the presence of the acid chyme from the 

 stomach, which acts on a product of the epithelial cells of the 

 duodenum known as prosecretin, changing it into secretin. When 

 secretin is absorbed by the blood and reaches the pancreas, it 

 stimulates this gland to secrete the pancreatic juice. It also 

 acts on the liver, causing that gland to secrete bile. Secretin 

 is not an enzyme, for it is not destroyed by heat. It cannot be 

 synthetized; in fact, little is known about its properties. To 

 date no substitute has been found. The presence and action of 

 secretin was first demonstrated by Bayliss and Starling who 

 injected into the circulation an extract made by washing scrapings 

 from the intestinal mucosa with weak hydrochloric acid. 



The average daily secretion of pancreatic juice by the ox is 3 

 to 4 pounds. It is strongly alkaline in reaction, due to sodium 

 carbonate, and has a specific gravity of about 1010. The im- 

 portant constituents are three enzymes — trypsin, amylopsin, 

 and steapsin. 



Trypsin is the most important pancreatic enzyme. It is 

 secreted in pro-enzymic form as trypsinogen, but is at once 

 activated by the enterokinase of the intestinal juice. It has the 

 power to change proteins into proteoses, peptones, and many 



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