170 EXPERIMENTS WITH PLANTS 



ration which soon occurs. Add a little alkali to the 

 mixture and shake again. Does it separate as before? 

 This is called an emulsion. Examine a drop of it under 

 the microscope. Notice the very small drops of fat 

 which float freely in the liquid. Compare the appearance 

 of milk under the microscope. The pancreatic juice is 

 alkaline and has the power of emulsifying fats. 



It also has a further action, which may be illus- 

 trated by melting a little cocoanut oil 1 (preferably on 

 a water-bath) and gradually adding a strong solution 

 of caustic soda, stirring it in the meanwhile. Very 

 soon a solid substance forms, whereupon the addi- 

 tion of soda may be stopped. On dissolving this 

 solid substance in water, we recognize from the 

 feeling, taste, odor and general behavior that it is 

 soap. Through the action of the alkali the oil has 

 been changed into soap and glycerine. A similar 

 reaction takes place in the presence of the pancreatic 

 juice: this reaction is due to a ferment called lipase 

 (steapsin), which attacks fats in the small intestine 

 and breaks them up into glycerine and fatty acids 2 

 which readily pass through the cell- walls and thus 

 become absorbed. 



Lipase is found in oil-containing seeds, especially 

 in the Castor-bean. If a few of the Castor-beans 

 (just sprouting) be crushed and added to fresh 



1 Obtainable at drug-stores. 



2 Lipase also has the power of causing these substances to unite so as to 

 form fats; its action is therefore said to be reversible. 



