DIGESTION 339 



juice is able of itself to form emulsions with perfectly neutral oils. 

 It is possible that the protein constituents of pancreatic juice 

 may have a share in emulsification, since the addition of protein 

 e.g., egg-white to a soap solution increases the stability of 

 the emulsions formed by the soap. In bile, on the contrary, 

 although the alkali is present, there is no fat-splitting ferment, 

 and according to the best experiments, bile alone has no emulsify- 

 ing power on perfectly neutral fat. But we now come to a re- 

 markable fact : this inert bile when added to pancreatic juice 

 greatly intensifies its emulsifying action, and a solution of bile- 

 salts has much the same effect as bile itself. The fact is un- 

 doubted, but the explanation is obscure. What it is that the 

 bile or bile-salts can add to the pancreatic juice which so increases 

 its power of emulsification, we do not know. It has been sur- 

 mised that a characteristic physical property of bile, the diminu- 

 tion of the surface-tension of watery liquids to which it is added, 

 may play an important part, perhaps, in enabling the fat- 

 splitting ferments or the emulsifying soaps to get into closer 

 contact with the unaltered fat. It is also true that bile by itself, 

 presumably in virtue of the chemical action of its alkaline salts, 

 can, in presence of a free fatty acid, rapidly form an emulsion. 

 But the pancreatic juice itself contains so considerable a quantity 

 of sodium carbonate that it would scarcely seem to require the 

 relatively feeble reinforcement of the alkaline salts of the bile. 



A part of the effect of the bile is certainly due to its favouring 

 the fat-splitting action of the pancreatic juice. By the addition 

 of bile, the quantity of fat split up by a definite amount of 

 dog's pancreatic juice may be increased two to threefold. It 

 has been shown that this is an action of the bile-salts. The 

 sodium salts of synthetically-obtained glycocholic and tauro- 

 cholic acids produce the same effect. The capacity of dissolving 

 soaps, which is a property of the bile-salts, is also of great im- 

 portance in supplementing the solvent power of the intestinal 

 liquids for the products formed by the pancreatic juice. The 

 solution of soaps in the bile-salts has the power in its turn of 

 dissolving free fatty acids. The significance of this in fat absorp- 

 tion will be referred to again. Although our knowledge of the 

 mutual action of the two juices on the digestion of fats is still 

 incomplete, there is no doubt that they are equally necessary. 

 For in some diseases of the pancreas fat or fatty acid often appears 

 in the stools, and this token of imperfect digestion of the fatty 

 food may be confirmed by the wasting of the patient. The same 

 may occur when the bile is prevented by obstruction of the duct 

 or by a biliary fistula from entering the intestine. Yet in some 

 cases of fistula, where there is every reason to believe that all 

 the bile is escaping externally, the nutrition of the patient at 



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