VI FAT EMULSIFIED 263 



duodenum, the pancreas conies into activity, its blood- 

 vessels dilate, it becomes red and full of blood, its cells 

 secrete rapidly, and a copious flow of pancreatic juice 

 takes place along its duct into the intestine. 



The secretion of bile by the liver is mu(?h more con- 

 tinuous than that of the pancreas, and is not so markedly 

 increased by the presence of food in the stomach. 

 There is, however, a store of bile laid up in the gall- 

 bladder ; and as the acid chyme pas.ses into the duodenum, 

 and flows over the common aperture of the bile and pan- 

 creatic ducts, a quantity of bile from this reservoir in the 

 gall-bladder is ejected into the intestine. The bile and 

 pancreatic juice together here mix with the chyme and 

 produce remarkable changes in it. 



In the first place, the alkali of these juices neutralises 

 the acid of the chyme ; in the second place, both the bile 

 and the pancreatic juice appear to exercise an influence 

 over the fatty matters contained in the chyme, which 

 facilitates the subdivision of these fats into very minute 

 separate particles, and this action is specially well-marked 

 when bile and pancreatic juice are mixed. The fat, as it 

 passes from the stomach, is very imperfectly mixed with 

 the other constituents of the chyme ; and the drops of fat 

 or oil (for all the fat of the food is melted by the heat of 

 the stomach) readily run together into larger masses. By 

 the combined action, however, of the bile and pancreatic 

 juice the larger drops of fat which pass into the intestine 

 from the stomach are etntdsified. that is to say are broken 

 up into exceedingly minute particles, and thoroughly 

 mixed with the rest of the contents ; they are brought in 

 fact to very much the same condition as that in which 

 fat {i.e. butter) exists in milk. When this emulsifying 

 has taken place the contents of the small intestine no 

 longer appear grey like the chyme in the stomach but 

 white and milky ; in fact it and milk are white for the 

 same reason, viz., on account of the multitude of minute 

 susperded fatty particles reflecting a great amount of light. 



