402 PRACTICAL PHYSIOLOGY 



the bile functionates as the channel by which the products of nervous 

 metabolism are removed. 



Inorganic Salts. These are chiefly sodium carbonate and disodium 

 hydrogen phosphate. 



The Uses of the Bile in Intestinal Digestion. (1) It is an alkaline 

 fluid, containing a viscid substance (mucin, etc.); consequently, it 

 assists in the emulsification of fats. 



EXPERIMENT VIII. Shake up some rancid oil with bile in a test 

 tube. Notice that a very stable emulsion is formed. (See Fats, p. 316.) 



(2) It causes a precipitate when added to an artificial peptic digest. 

 EXPERIMENT IX. Add some bile to a sample of a 24 hours' peptic 



digestion of egg-white. A precipitate of proteins is produced. 



It is claimed that by this precipitation the fluid chyme becomes much 

 thicker, and its condition, therefore, rendered more favourable for being 

 further digested in the intestine, since it will adhere to the intestinal 

 wall. 



(3) It dissolves the free fatty acid produced in the intestine. 



On account of this latter action, and, to a certain extent, on account 

 of its emulsifying powers, bile assists materially in the absorption of 

 fat. Where bile is not excreted into the intestine (as in Jaundice), the 

 faeces become rich in fatty acid, in consequence of which they appear 

 greasy and pale in colour. The presence of excess of fatty material in 

 the intestinal contents also hinders protein digestion to a certain 

 extent, by coating the particles of food and preventing the juices 

 getting at them. In consequence of this, bacterial growth becomes 

 excessive when there is suppression in the secretion of bile. It is by 

 this means that bile diminishes putrefaction in the intestine, and not on 

 account of any antiseptic properties it possesses, for bile itself quickly 

 becomes putrid on standing. Many other properties have been ascribed 

 to bile, e.g. that it assists the absorption of oil globules and that it acts 

 as a laxative, but these are not of much importance. It may be men- 

 tioned that in some animals bile contains a diastatic ferment. The 

 secretion of bile by the liver is stimulated by the intravenous injection 

 of secretin. It also activates, to a certain extent at least, the lipolytic 

 ferment of pancreatic juice. 



To sum up, we may state that, although bile contains no ferment by 

 which a chemical change can be produced on any of the food-stufls, it is 

 nevertheless of great value as a digestive fluid, in that it assists the 

 pancreatic juice: (1) by neutralising the chyme; (2) by activating 

 pancreatic lipase ; (3) by dissolving the fatty acid produced by the 

 action of lipase ; (4) by assisting in the emulsification of neutral fat ; 

 (5) by assisting the absorption of fat; and consequently (6) of allowing 



