X 



34 HUMAN PHYSIOLOGY. 



When starch is subjected to the action of the juice, it is at once transformed 

 into glucose ; the change takes place more rapidly than when saliva is 

 added. This action is caused by the presence of a special ferment, amyl- 

 opsin. 2d. Upon albumen. The albuminous bodies are changed by the 

 juice into, first, an alkali albumen, and then into peptone. The albumen 

 does not swell up, as is the case in gastric digestion, but is gradually cor- 

 roded and dissolved. This change is due to the presence of the ferment, 

 trypsin. Long- continued action of trypsin converts the peptones into two 

 crystalline bodies, leucine and tyrosin. 3d. Upon fats. The most striking 

 action of the pancreatic juice is the emulsification of the fats or their sub- 

 division into minute particles of microscopic size. This change takes place 

 rapidly and depends upon the alkalinity of the fluid and the quantity of 

 albumen present, combined with the intestinal movements. The neutral 

 fats are also decomposed into their corresponding/^/// acids and glycerine ; 

 the acids thus set free unite with the alkaline bases present in the intestine 

 and form soaps. This decomposition of the neutral fats is caused by the 

 ferment, steapsin. 4th. Upon cane sugar the juice also exerts a special 

 influence, converting it readily into glucose. 



The total quantity of this fluid secreted in twenty-four hours has not 

 been accurately determined ; it varies from one to two pounds ; it is poured 

 out most abundantly an hour after meals. 



The Bile has an important influence in the elaboration of the food and 

 its preparation for absorption. It is a golden-brown, viscid fluid, having a 

 neutral or slightly alkaline reaction and a specific gravity of 1 .020. 



COMPOSITION OF BILE. 



Water 859.2 



Sodium glycocholate \ 



Sodium taurocholate J 



Fat 9.2 



Cholesterine 2.6 



Mucus and coloring matter 29.8 



Salts 7.8 



The Biliary salts, sodium glycocholate and taurocholate, are character- 

 istic ingredients, and are formed in the liver by the process of secretion, 

 from materials furnished by the blood. It is probable that they are derived 

 from the nitrogenized compounds, though the stages in the process are 

 unknown. They are reabsorbed from the small intestine to play some 

 ulterior part in nutrition. 



