362 DIGESTION 



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 emulsifying power on 

 perfectly neutral fat. 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 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 surmised that a characteristic physical 

 property of bile, the diminution 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, 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 rela- 

 tively feeble reinforcement of the alkaline salts of the bile. 



An important 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 taurocholic acids 

 produce the same effect. It is in virtue of this action that the bile- 

 salts are sometimes spoken of as the co-ferment of the lipase. As 

 already pointed out, this action is exerted in presence of the fully 

 formed enzyme, and should not be confounded with the effect of the 

 bile- salts in activating the lipase zymogen. The capacity of dis- 

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

 importance 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 dis- 

 solving free fatty acids. The significance of this in fat absorption 

 will be referred to again. A further illustration of the mutual 

 adaptation of the various digestive juices, of the remarkably precise 

 manner in which the action of each dovetails into the action of 

 others, is afforded by the facts already mentioned in connection with 

 the lipase of the stomach. It is highly probable that the fatty acids 

 formed by the gastric lipase, even if formed only in small amount, 

 may exertan important influence in emulsifying the fat as soon as it 

 enters the intestine. The intestinal juice itself also unquestionably 

 takes a share in the digestion of fat along with the pancreatic 

 secretion and the bile. There exists also, as will be seen later on, a 



