CHEMISTRY OF DIGESTION AND NUTRITION. 307 



of soap, mucilage, etc. Milk is a natural emulsion that separates partially 

 on standing, some of the oil rising to the top to form cream. Bernard made 

 the important discovery that when oil and pancreatic juice are shaken together 

 an emulsion of the oil takes place very rapidly, especially if the temperature 

 is about that of the body. The main cause of the em unification has been 

 shown to be the formation of free fatty acids due to the action of steapsin, 

 and the union of these acids with the alkaline salts present to form soaps. 

 This fact has been demonstrated by experiments of the following character: 

 If a perfectly neutral oil is shaken with an alkaline solution (} per cent, 

 sodium-carbonate solution), no emulsion occurs and the two Liquids soon sepa- 

 rate. If to the same neutral oil one adds a little free fatty acid, or if one 

 uses rancid oil to begin with and shakes it with \ per cent, sodium-carbonate 

 solution, an emulsion forms rapidly and remains for a long time. Oil con- 

 taining fatty acids when shaken with distilled water alone will not give an 

 emulsion. It has been shown, moreover, by Gad and Ratchford that with a 

 certain percentage of free fatty acids (5J per cent.) rancid oil and a sodium- 

 carbonate solution will form a fine emulsion spontaneously — that is, without 

 shaking. Shakino- however, facilitates the emulsification when the amount 

 of free acid varies from this optimum percentage. In what May the formation 

 of soaps in an oily liquid causes the oil to become emulsified is still a matter 

 of speculation. The splitting of the oil into small drops seems to be caused, 

 in cases of spontaneous emulsification, by the act of formation of the soap — 

 that is, the union of the alkali with the fatty acid — in other cases by the 

 mechanical shaking, or by these two causes combined. The application of 

 these facts to the action of the pancreatic juice in the small intestine is 

 easily made. When the chyme, containing more or less of liquid fat, comes 

 into contact with the pancreatic juice, a part of the oil is quickly split by the 

 steapsin, with the formation of free fatty acids. These acids unite with the 

 alkalies and the alkaline salts present in the secretions of the small intestine 

 (pancreatic juice, bile, intestinal juice) to form soaps. The formation of the 

 soaps, aided, perhaps, by the peristaltic movements of the intestine, emulsifies 

 the remainder of the fats and thus prepares them for absorption or further 

 saponification. It has been suggested that the proteids in solution in the 

 pancreatic juice aid in the emulsification, but there is no experimental evi- 

 dence to show that this is the ease. A factor of much more Importance is 

 the influence of the bile. In man the pancreatic juice and the bile are poured 

 into the duodenum together, and in all mammals the two secretions are mixed 

 with the food at some part of the duodenum. Now, it has been shown 

 beyond question that a mixture of bile and pancreatic juice will cause a 

 splitting of fats into fatty acids and glycerin much more rapidly than will the 

 pancreatic juice alone. 1 This effect of the bile is not due to the presence in 

 it of a fat-splitting enzyme of its own : the bile seems merely t" favor in 

 some way the action of the steapsin contained in the pancreatic secretion. 



1 Nencki : Archiv fiir experimenfelU Pathologic ». Pharmakologie, 1886, Bd, 20, S. 367; Ratch- 

 ford: Journal of Physiology, 1891, vol. 12, p. 27. 



