314 A MANUAL OF PHYSIOLOGY 



ferment which can split up neutral fats and set free fatty 

 acids, and an alkali which can combine with those acids to 

 form soaps. Accordingly, pancreatic juice is able of itself 

 to form emulsions with perfectly neutral oils. It is possible 

 that the proteid constituents of pancreatic juice may have a 

 share in emulsification. 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 emulsi- 

 fying power. But we now come to a remarkable 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 undoubted, but 

 the explanation is obscure. What it is that bile or bile-salts 

 can add to the pancreatic juice which so increases its power 

 of emulsification, we do not know. It is indeed true that 

 the bile, presumably in virtue of its alkaline salts, can, in 

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

 the pancreatic juice itself contains a considerable quantity of 

 sodium carbonate. 



A part of the effect of the bile seems to be due to its 

 favouring in some way the fat-splitting action of the pan- 

 creatic juice. The capacity of dissolving soaps, which is a 

 property of the bile-salts, appears also to be important in 

 supplementing the solvent power of the intestinal liquids for 

 the soaps formed by the pancreatic juice. But however the 

 mutual action of the two juices on the digestion of fats may 

 be explained, there is no doubt that they are equally neces- 

 sary. 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 ; and the same occurs when the bile is pre- 

 vented by obstruction of the duct or by a biliary fistula from 

 entering the intestine. 



The white stools of jaundice owe their colour, not merely to the 

 absence of bile-pigment, but also to the presence of fat. Their 

 highly offensive odour used to be adduced as evidence that bile is 

 the ' natural antiseptic ' of the intestine. It seems rather to be due 

 to the coating of the particles of food with undigested fat, which 

 shields the proteids from the action of the digestive juices while 



