234 PRACTICAL PHYSIOLOGY 



acetic acid. A precipitate of alkali meta-protein results (for 

 Reactions, see p. 202). 



Apply to another sample the tests for proteoses and peptones, 

 and note that they are positive. 1 



EXPERIMENT II. If the pancreatic extract in Experiment I be 

 boiled before the fibrin is added, no digestion will result. The 

 digestive agent is, therefore, a ferment which is destroyed by heat. 



EXPERIMENT III. Repeat Experiment I, making the reaction 

 acid by means of hydrochloric acid. Note that, although the fibrin 

 becomes swollen up as this depends on the acid, not on the fer- 

 ment no formation of proteoses or peptone occurs. The trypsin 

 cannot act in acid medium, being destroyed in this reaction. 



Trypsin can carry digestion further than pepsin. Allow a digest 

 to go on for twenty-four hours or longer. Filter and evaporate to 

 small bulk some of the filtrate. Take a drop of this concentrated 

 filtrate and allow it to dry on a microscopic slide ; examine the 

 crystals of leucine and tyrosine present, noting that the former con- 

 sist of round balls frequently with concentric markings and yellowish 

 in colour, whereas the latter are usually grouped into sheaves of 

 needles (see Fig. 177). Test the filtrate for protein by the biuret 

 test. Also test it by adding some drops of chlorine or bromine 

 water. Note the red colour which results due to the presence of 

 tryptophan. 



Diastase. The old name for pancreatic diastase is Amylopsin. 

 This ferment acts on starch in a way similar to ptyalin, i.e. it 

 converts starch into dextrines and maltose. It can act on unboiled 

 starch. 



EXPERIMENT IV. Take four test tubes a, 6, c and d. Into a 

 place 5 c.c. of a suspension of starch; into the other three tubes 

 put 5 c.c. of boiled starch solution. Add to a, b and c a few drops 

 of pancreatic extract (glycerine extract is good) and to d a similar 

 amount of boiled pancreatic extract. Add to tube c in addition 

 a trace of sodium chloride. Place all four tubes in a water- bath 

 at 40 C. Remove drops from time to time and test on a porcelain 

 slab with iodine. When all colour disappears, test contents of the 

 tubes by Fehling's test. 



Lipase. The old name for pancreatic lipase is Steapsin. This 

 ferment breaks down neutral fat into fatty acids and glycerol 

 (see p. 222). 



EXPERIMENT V. Take two large test tubes and into each place 

 about 10 c.c. of neutral cream (i.e. cream to which a few drops of 

 an alcoholic solution of phenolphthalein has been added, and then 



- NaOH until a definite red colour appeared). Add to one test 



tube a few drops of fresh watery pancreatic extract and to the 

 other a few drops of boiled extract ; then make the contents definitely 



1 No primary proteose is formed by tryptic digestion ; there is, however, a 

 considerable amount of secondary proteose (see p. 203). 



