DETERMINING BIOLOGICAL ACTIVITIES OF BACTERIA 201 



Enzyme Action. 4 The action of the enzymes produced by bac- 

 teria may be demonstrated by bringing the bacteria, or their isolated 

 ferments, into contact with the proper substances and observing 

 both the physical and chemical changes produced. In obtaining 

 enzymes free from living bacteria, it is convenient to kill the cultures 

 by the addition either of toluol or of chloroform. Both of these 

 substances will destroy the bacteria without injuring the enzymes. 

 Enzymes may also be obtained separate from the bodies of the 

 bacteria by nitration. 



PROTEOLYTIC ENZYMES. The most common evidences of proteo- 



T 



FIG. 28. TYPES OF GELATIN LIQUEFACTION BY BACTERIA. 



lytic enzyme action observed in bacteriology are the liquefaction 

 of gelatin, fibrin or coagulated blood-serum, and the peptonization 

 of milk. This may be observed both by allowing the proper bacteria 

 to grow upon these media, or by mixing sterilized cultures with 

 small quantities of these substances. 5 The products of such a reac- 

 tion may be separated from the bacteria by filtration and then tested 

 for pepton by the biuret reaction. 



4 See also pp. 54 et seq. 



8 Bitter, Archiv f. Hyg., v. 1886. 



