THE FOOD AND DIGESTION 347 



series of bodies which no longer give the biuret test. These 

 consist chiefly of the component amido - acids, of which 

 the most important are leucin and tyrosin, and ammonia 

 compounds (see p. 11). 



Tryptophan. If chlorine water is added to a pancreatic 

 digestion, which has proceeded for a long time, a rose-red 

 colour is struck, and the substance yielding this, to which 

 the name of tryptophan has been given, appears to be amido- 

 acetic acid linked to skatol (see p. 399). 



While trypsin has the power of splitting some of the 

 peptone in the manner indicated, it has probably little 

 opportunity of doing so in the intestine, because the proteid 

 is rapidly absorbed as it is changed to peptone. 



On nucleo - proteids the trypsin acts by digesting the 

 proteid and dissolving the nucleic acid so that it can be 

 absorbed. 



On collagen and elastin the trypsin has little action ; but 

 on gelatin it acts as upon proteids. 



2nd. An Amylolytic Enzyme Amylopsin. This acts in 

 the same way as ptyalin, but more powerfully, converting a 

 certain part of the maltose into dextrose. It acts best in a 

 faintly acid medium. 



3rd. A Fat Splitting Enzyme Pialyn. This is the most 

 easily destroyed and the most difficult to separate of the 

 zymins. It breaks the fats into their component glycerin and 

 fatty acids. The fatty acid links with the alkalies which are 

 present to form soaps, and in this form, or dissolved as free 

 fatty acids in the bile, they are absorbed. But the formation 

 of soaps also assists the digestion of fats by reducing them 

 to a state of finely divided particles, an emulsion upon which 

 the pialyn can act more freely. This process of emulsifica- 

 tion is assisted by the presence of proteid in the pancreatic 

 juice and also by the presence of bile. 



That these enzymes are independent of one another is 

 shown by many facts. 



1. Amylopsin does not appear till a month after birth. 



2. Amylopsin is taken up by dry glycerin while trypsin 

 is not. 



3. Trypsin may be precipitated and separated by shaking 

 with collodion. 



