I 4 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



than that of the control and finally *2N alkali is added until the 

 colour matches that of the control. To the control solution two drops 

 of *2N alkali are now added so as to produce a deep red colour, and 

 alkali is added to the solution until it attains the same deep red colour. 

 The difference between the alkali and acid used in the solution and in 

 the control (from 0-0-2 c.c.) gives the titration figure. 



(h) Hydrolysis with Enzymes. 



Hydrolysis by the action of proteoclastic enzymes is never com- 

 plete. The earlier investigators always observed that a complex 

 body antipeptone resistant to the further action of trypsin was 

 formed. Fischer and Abderhalden [1903, I, 2] have confirmed this 

 observation and have found that the resistant body contains all the 

 phenylalanine and proline present in the protein molecule ; even by 

 the combined action of pepsin and trypsin, although phenylalanine 

 and proline are formed under these conditions, a body resistant to 

 hydrolysis by trypsin still remained. Almost complete hydrolysis 

 may be effected by trypsin and the enzymes in the small intestine 

 if a sufficiently long time be given for the digestion. 



Henriques and Gjaldbak [1910] estimated the amount of unhydro- 

 lysed protein, and found that in a prolonged digestion some 5-10 

 per cent, of the amino nitrogen still remained in combination. 



Hydrolysis by enzymes, though of use in the discovery of new 

 units in the protein molecule, is not serviceable for a complete analysis 

 of the decomposition products. . 



