DEFENSIVE FERMENTS OF THE ANIMAL ORGANISM 49 



shown that many processes go on exactly in the same 

 way, qualitatively, as if the cell were intact. But the 

 principal life process, the oxidation to carbon dioxide 

 and water, is not found. Even slight injuries to the 

 cells are sufficient to annul this important process. 

 In such a juice it may be said that only the 

 preparative functions remain all of them processes 



which we usually ascribe to ferments. If to the juice 



j j 



obtained in this manner a peptone containing very 

 sparingly soluble amino-acids is added as, for 

 instance, tyrosin or cystin or else a kind of peptone 

 in the building up of which an amino-acid takes 

 part and this may be easily detected at the moment 

 of decomposition by means of a colour reaction 5 

 then it is very easy to ascertain whether the juice con- 

 tains any ferment that is capable of splitting the 

 peptone in question. The precipitation of the respec- 

 tive amino-acids, or the appearance of the colour 

 reaction, announces the presence of the decomposing 

 agent. 



Still more conclusive results are obtained if comr 

 binations of a know^n structure for instance, poly- 

 peptides, in the building up of which the above- 

 mentioned amino-acids take active part- -be chosen 

 for the experiment. Or one may follow the decom- 

 position in a polariscope tube. A certain quantity of 



5 This is the case, for instance, with tryptophane. 

 4 



