172 FUNCTIONS OF NUTRITION. 



oily portion of the food is altered in appearance, being converted into 

 a white, opaque emulsion, termed chyle, always found during digestion 

 entangled among the valvulae conniventes, and adhering to the surface 

 of the small intestine. The digestion of fatty substances consists 

 mainly in this emulsion, by which they are converted into chyle and 

 made ready for absorption. As the change begins to take place in the 

 duodenum, immediately below the orifice of the pancreatic duct, this 

 circumstance points to the pancreatic juice as the main agent in the 

 formation of chyle. But in most animals the biliary duct opens into 

 the intestine at nearly the same point, and it might therefore be 

 questioned whether the bile has not an equal share in the result. This 

 doubt was removed by the experiments of Bernard on the rabbit. In 

 this animal, the biliary duct opens, in the usual manner, just below 

 the pylorus, while the pancreatic duct communicates with the intestine 

 30 or 40 centimetres farther down ; so that there is a considerable 

 extent of the small intestine containing bile, into which the pancreatic 

 juice has not yet been discharged. Bernard fed these animals with 

 substances containing oil, or injected melted butter into the stomach; 

 and, on killing them afterward, found no chyle in the intestine 

 between the openings of the biliary and pancreatic ducts, while it 

 was abundant immediately below the orifice of the latter. Above 

 this point the lacteal vessels were empty or transparent, while below 

 it they' were full of opaque chyle. These experiments, which were 

 confirmed by Jackson,* show that the emulsifying action of the 

 pancreatic juice on oily matters is exerted within the body during 

 digestion, and that it is the direct agent in the production of chyle in 

 the intestine. 



It is probable that the acidifying action of pancreatic juice on fats 

 is less extensive during digestion than its emulsive effect. These two 

 properties of the secretion, when examined in the test-tube, show a dif- 

 ference in their mode of action. The emulsification of fat, when in contact 

 with pancreatic juice, is instantaneous and complete ; but its acidifi- 

 cation requires a longer time, and increases progressively for some 

 hours. A partial acidification and saponification undoubtedly takes 

 place in the duodenum ; but the greater part of the fat remains in the 

 form of an emulsion, and the absorption of chyle begins immediately 

 below the orifice of the pancreatic duct, as shown by the condition of 

 the lacteal vessels. The chyle in the lacteal vessels is mainly com- 

 posed of undecomposed fat ; and, according to Hoppe-Seyler, the quan- 

 tity of saponified fat, in both the intestine and the lacteals, is compara- 

 tively insignificant. 



The second important action of the pancreatic juice in digestion is 

 the transformation of starch into glucose. It is much more effective 

 in this respect than the saliva, being almost instantaneous, and con- 

 verting the whole of the starch at once, while that of the saliva is 



American Journal of the Medical Sciences. Philadelphia, October, 1854. 



