ELEMENTAKY PHYSIOLOGICAL CHEMISTEY 235 



Lecithin (CJEgoNPO,,) and Cholesterin (C 27 H 45 OH) (see Lesson III.) 

 These two bodies are kept in solution in the bile by means of the 

 bile salts. 



EXPERIMENT VI. Place some bile in a test-tube, and add one or two 

 crystals of cholesteriri to it and gently warm. The cholesterin dissolves. 



Repeat this experiment with water, when the crystals will not 

 dissolve. 1 



Both lecithin and cholesterin are excretory products. The tissues 

 which contain the highest percentage of them are the nervous, so that 

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

 metabolism are removed. 



Inorganic Salts. These are chiefly sodium carbonate (Na 2 Co 3 ) and 

 disodium hydrogen phosphate (Na HP0 4 ). 



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 emulsifi cation of fats. 



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

 Notice that a very stable emulsion is formed. (See Fats). 



(2) In virtue of the bile salts which it contains, (a) it precipitates 

 syntonin, and (b) to a certain extent also, proteoses and pepton. 



EXPERIMENT VIII. Add to a sample of a 24 hours' peptic digestion 

 of egg-white some bile, from which the mucin has been removed by 

 alcohol. A precipitate of syntonin, etc., is produced. 



Thus the fluid chyme becomes much thicker on mixing with the bile, 

 and its condition, therefore, more favourable for being further digested 

 in the intestine, since it will adhere to the intestinal wall. 



(c) 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, it assists materially in the 

 absorption of fat. Where bile is not excreted into the intestine 

 (as in Jaundice), the faeces become rich in fat, in consequence of 

 which they appear greasy and pale in colour. The presence of 

 excess of fat in the intestinal contents also hinders, to a certain 

 extent, proteid digestion by coating the particles of food and preventing 

 the juices getting at them. In consequence of this, bacterial growth 

 becomes excessive. 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 digestive properties have been ascribed to bile, e.g. that it assists 



1 These two bodies are also kept in solution in the blood because of the presence 

 of bile salts. 



