DIGESFION. 683 



the enzyme having been destroyed by heat. (The pancreatin solution itself 

 should be tested with Fehling's solution, as the commercial article is frequently 

 adulterated with sugar.) 



Steapsin (lipase) splits the neutral fats into fatty acids and glycerin. 

 The liberated fatty acids combine with alkali of the pancreatic juice, 

 forming soap. The action of lipase is materially aided by the pres- 

 ence of bile, although it is not understood how this occurs. 



Experiment 82. (Fat-splitting action of steapsin.} (Fresh pancreas must be 

 used for the experiment.) Shake about 2 grammes of butter with a few c.c. of 

 lukewarm water, to which a drop of caustic soda solution has been added. 

 After cooling shake with an equal volume of ether, pour the ethereal solution 

 on a watch-glass and allow the ether to evaporate. To the neutral butter fat 

 thus obtained add a piece of fresh pancreas the size of a pea, mix the materials 

 intimately by rubbing, and place in a thermostat at 40 C. (104 F.). After a 

 few minutes the odor of butyric acid will be recognized. 



Shake a gramme of butter fat, obtained as above, with about 5 c.c. of luke- 

 warm water, render slightly alkaline with sodium carbonate, using rosolic acid 

 as an indicator, add some fresh pancreas converted into a thin paste by grind- 

 ing with water, and keep the mixture at 40 C. (104 F.) for twelve hours. 

 Notice that the mixture turns yellow, due to the acid liberated from the butter 

 fat. The experiment when made with boiled pancreas does not show liberation 

 of acid. 



Trypxin breaks down proteins by a series of changes almost iden- 

 tical with those produced by pepsin. It is, however, most active in 

 an alkaline medium, and has a more rapid and complete action than 

 that of pepsin. The digestions by pepsin and trypsin are to a certain ex- 

 tent supplementary to each other, for it is found that proteins subjected 

 to both are more thoroughly decomposed than by either one alone. 

 Under normal conditions it is probable that tryptic digestion produces 

 a considerable amount of amino-bodies, and that the remainder of the 

 peptones and proteoses are split up by the intestinal enzyme, erepsin. 



Experiment 83. (Artificial tryptic digestion.} To 250 grammes of protein add 

 a solution of 5 grammes of sodium carbonate, 3 grammes of pancreatin, and 

 5 c.c. of chloroform. Keep in a thermostat at 40 C. (104 F.) for ten days. 

 Then filter off a few c.c. of the liquid and add bromine-water. A violet color 

 is produced, due to tryptophane. Acidify the digested mixture with acetic 

 acid, boil, filter, evaporate filtrate to 150 c.c., and allow to stand in a cool 

 place. In a few hours crystals of tyrosine will be deposited. Decant the 

 mother-liquor and purify the tyrosine by recrystallizing from a solution con- 

 taining a little ammonia. Use the crystals to test for tyrosine (see Index). 



Evaporate the mother-liquor from the tyrosine to a thin syrup, add 200 c.c. 

 of hot alcohol, allow the mixture to cool, and filter. Evaporate the filtrate to 

 dryness, dissolve the residue in water, and boil with freshly prepared lead 

 hydroxide. Allow to cool, filter, free the filtrate from lead by means of 



