DIGESTION. H3 



the intestine, is identical with that for the secretion of pancreatic 

 juice, and that in each case secretin formed by the action of hydro- 

 chloric acid on the duodenal epithelium is absorbed, and excites the 

 liver and pancreas to increased activity. 



Barbera has shown that a meat-diet excites the greatest secretion 

 of bile, fat less, and a carbohydrate diet hardly any. 



It is in the intermission between meals that the liver is least 

 active, and it is then that only a small supply reaches the duodenum. 

 It continues during pains the most violent, in intestinal congestion, 

 and in peritoneal inflammations. 



Contrary to the plan of all the other secreting and excreting 

 organs, the main supply of blood to the liver, and from which its secre- 

 tion, the bile, is formed, is venous: from the portal vein. The nutrient 

 function of the hepatic artery is to supply structures and membranes 

 only. Since the portal vein furnishes the supply, the bile is secreted 

 at a very much lower pressure and therefore more slowly than those 

 secretions from glands whose supply is arterial, as the pancreas and 

 salivary glands. It is quite natural that a fluid so complex as the 

 bile demands for its preparation a much longer period of time than 

 one which contains . only water, salts, and certain principles of the 

 blood. Though not directly governed by nerve-influences upon the 

 portal vein, the blood-supply to the liver is varied. 



Compared with the size of the liver, the secretion is small and 

 slow, and holds but little relation to the mass of blood traversing it. 

 The quantity secreted per diem has been variously computed at two 

 pounds. Its specific gravity in man averages 1.026 ; reaction, neutral 

 or slightly alkaline. 



Chemical Properties and Constituents of the Bile. 



Bile mixes with water, producing no turbidity ; heat produces no 

 coagulation because of the absence of any coagulable proteids. Alco- 

 hol precipitates mucin, diastase, and bilirubin, if the latter is present. 

 Acetic acid precipitates mucus ; lead acetates, the biliary salts. When 

 in contact, bile rapidly destroys the red blood-corpuscles. 



Bile contains both organic and inorganic materials. Those or- 

 ganic are mucin, biliary pigments, biliary salts, cholesterin. lecithin, 

 neutral fats, soap, urea, and diastase. In organic matters are water, 

 chloride of sodium, and phosphates of iron, calcium, and magnesium. 



The means by which the various components of the bile are 

 formed is as yet not thoroughly understood. Some of its constituents 

 may exist in the portal blood; thus the pigment is produced by the 



