CH. VI.] EMULSIFICATION. 157 



fat in the small intestine is thus emulsified as a preliminary 

 to complete hydrolysis by the pancreatic lipase. 



The digestion of fats. 



The fats are hydrolysed to a small extent in the stomach 

 by gastric lipase. This action is greater if the fat be given 

 in an emulsified form, as in milk. 



In the duodenum, the fat mixed with the fatty acid is 

 spontaneously emulsified by the alkaline bile, succus 

 entericus and pancreatic juice. The emulsified fat is then 

 completely hydrolysed to glycerol and fatty acids by the 

 pancreatic lipase. The fatty acids are converted into 

 soluble soaps by the alkalies present. The soaps and 

 glycerol are absorbed into the epithelial cells bordering the 

 villi, where they are resynthesised into fats. These are 

 passed into the lacteals, and reach the blood stream by way 

 of the thoracic duct. 



164. (a) Carefully allow a drop of neutral olive oil to fall 

 gently on to the surface of some 0*25 per cent, sodium carbonate 

 contained in a watch-glass. The drop of oil remains quite clear, and 

 forms a thin (circular) film on the surface. 



(b) Shake 4 cc. of neutral oil with 3 drops (only) of oleic acid in a 

 dry test-tube. With a drop of this mixture repeat (a), using a 

 fresh watch-glass full of Na 2 CO 3 . The rancid oil slowly spreads out 

 in an amoeboid fashion and becomes converted into a milky emul- 

 sion. 



(c) To the remainder of the mixture of oil and oleic acid add 

 12 more drops of oleic acid, shake well, and repeat the experiment. 

 The drop becomes white and opaque, but does not become emulsified. 



NOTES. i . It is absolutely essential that the oil be quite neutral, and this 

 can best be tested by dropping it on to 0-25 per cent. Na 2 CO 3 . If a spontaneous 

 emulsion is formed, a fresh sample must be obtained, or melted fresh butter 

 substituted. 



2. The spontaneous emulsion in (b) is caused by the trace of oleic acid 

 dissolving in the alkali to form a soap, diffusion currents being thus set up 

 which divide the fat into microscopic droplets. 



3. It is important to mix the oil very thoroughly with the oleic acid. 



4. In (c) the large excess of oleic acid leads to the opaque ring of soap 

 being formed round the oil, and this soap, being only slightly soluble in water, 

 prevents the formation of an emulsion. 



