BILE, PANCREATIC JUICE, AND SUCCUS ENTERICUS. 281 



The decomposition of the bile acids into cholalic acid and tauriu or glycin 

 respectively takes place naturally in the intestine, the glyciii and taurin 

 being probably absorbed, so that from the two acids, after they have served 

 their purpose in digestion, the two ammonia compounds are returned into 

 the blood. Each of the two acids, or cholalic acid alone, when treated with 

 sulphuric acid and cane-sugar, gives a magnificent purple color (Petten- 

 kofer's test), with a characteristic spectrum. A similar color may, however, 

 often be produced by the action of the same bodies on albumin, amyl alcohol, 

 and some other organic bodies. 



216. Action of bile on food. In some animals at least bile contains a 

 ferment capable of converting starch into sugar ; but its action in this respect 

 is wholly subordinate. 



On proteids bile has no direct digestive action whatever, but being, gen- 

 erally at least, alkaline, and often strongly so, tends to neutralize the acid 

 contents of the stomach as they pass into the duodenum, and, as we shall 

 see, so prepares the way for the action of the pancreatic juice. To peptic 

 action it is distinctly antagonistic ; the presence of a sufficient quantity of 

 bile renders gastric juice inert toward proteids. Moreover, when bile, or a 

 solution of bile-salts, is added to a fluid containing the products of gastric 

 digestion, a precipitate takes place, consisting of parapeptone (when present), 

 peptone, pepsin, and bile-salts. The precipitate is redissolved in an excess 

 of bile or solution of bile-salts ; but the pepsin, though redissolved, remains 

 inert toward proteids. This precipitation actually does take place in the 

 duodenum, and we shall speak of it again later on. 



With regard to the action of bile on fats, the following statements may 

 be made : 



Bile has a slight solvent action on fats, as seen in its use by painters. It 

 has by itself a slight but only slight emulsifying power ; a mixture of oil 

 and bile separates after shaking rather less rapidly than a mixture of oil and 

 water. With fatty acids bile forms soap. It is, moreover, a solvent of solid 

 soaps, and it would appear that the emulsion of fats is under certain circum- 

 stances at all events facilitated by the presence of soaps in solution. Hence 

 bile is probably of much greater use as an emulsion agent when mixed with 

 pancreatic juice than when acting by itself alone. To this point we shall 

 return. Lastly, the passage of fats through membranes is assisted by wetting 

 the membranes with bile or with a solution of bile-salts. Oil will pass to a 

 certain extent through a filter-paper kept wet with a solution of bile-salts, 

 whereas it will not pass or passes with extreme difficulty through one kept 

 constantly wet with distilled water. 



Bile possesses some antiseptic qualities. Out of the body its presence 

 hinders various putrefactive processes; and when it is prevented from flow- 

 ing into the alimentary canal, the contents of the intestine undergo changes 

 different from those which take place under normal conditions, and leading 

 to the appearance of various products, especially of ill-smelling gases. 



These various actions of bile seem to be dependent on the bile-salts and 

 not on the pigmentary or other constituents. 



Pancreatic Juice. 



217. Natural healthy pancreatic juice obtained by means of a tem- 

 porary pancreatic fistula differs from the digestive juices of which we have 

 already spoken in the comparatively large quantity of proteids which it con- 

 tains. Its composition varies according to the rate of secretion, for, with the 

 more rapid flow, the increase of total solids does not keep pace with that of 

 the water, though the ash remains remarkably constant. 



