CHAP, i.] TISSUES AND MECHANISMS OF DIGESTION. 449 



the pancreatic juice. To peptic action it is distinctly antagonistic; 

 the presence of a sufficient quantity of bile renders gastric juice inert 

 towards 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 such bye-products as may be 

 present, of peptone, pepsin and bile-salts. The precipitate is redis- 

 solved in an excess of bile or solution of bile-salts ; but the pepsin 

 though redissolved remains inert towards proteids. This precipi- 

 tation 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 state- 

 ments 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 separate after shaking rather 

 less rapidly than a mixture of oil and water. With fatty acids 

 bile forms soaps. 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, where- 

 as 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 flowing 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. 



248. Natural healthy pancreatic juice obtained by means of 

 a temporary pancreatic fistula differs from the digestive juices of 

 which we have already spoken, in the comparatively large quantity 

 of proteids which it contains. 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. 



By an incision through the linea alba the pancreatic duct (or ducts) 

 can easily be found either in the rabbit or in the dog, and a cannula 

 secured in it. There is no difficulty about a temporary fistula; but 



