THE DIGESTIVE SYSTEM. 179 



3. The pancreatic juice also acts on the fats in two 

 ways : 



(a) It emulsifies them, i.e. the fat is divided into exceed- 

 ingly fine drops, each enveloped in a coating of albuminous 

 substance. An emulsion can be made artificially by shak- 

 ing together water, oil, and white of egg. The shaking 

 breaks the oil into fine drops, which would soon gather 

 again if no other substance were present ; but it is sup- 

 posed that the albumen forms a thin coating around each 

 droplet, enabling it to remain distinct in the liquid. 



(b) The fats are also acted on chemically by steapsin, 

 another ferment of the pancreatic juice ; they are decom- 

 posed with the formation of free fatty acids, and thus 

 more fully prepared to be absorbed and to build up the 

 tissues. These free fatty acids aid in the work of emulsi- 

 fying the rest of the fat. 



Review of Digestive Liquids. Saliva acts only on 

 starch, gastric juice on proteids, bile on fats, whereas 

 pancreatic juice acts on all three, and, probably, more 

 energetically than the above-named liquids. 



Intestinal Juice. The intestinal juice contains a fer- 

 ment, called invertin, which changes cane sugar to dextrose 

 which is a variety 

 of grape sugar. vim 



Acids and Al- 

 kalies in Diges- 

 tion. The bile 



and the pancreatic intestinal cianc-s 



juice are alkaline, 



Fig. 64. Mucous Membrane of Small Intestine 



and overcome the 



acidity of the chyme, as the acidity of the gastric juice 



in the stomach overcame the alkalinity of the saliva. 



