98 THE ACTION OF ENZYMES 



production altogether ; on the other hand, lactose has 

 little effect. A small amount of quinine can prevent 

 enzyme formation by Bact. pyocyaneum without inter- 

 fering much with the growth of the organism. 



Although the formation of enzymes may be said to 

 be characteristic of certain species, many bacteria lose 

 this power when cultivated for a long time under some- 

 what abnormal conditions. 



To determine the presence of a enzymes in a culture 

 of any organism grown in broth, milk, or other liquid 

 medium, it is necessary first to remove the living organ- 

 isms or check their development, after which the action 

 of the solution may be tested upon gelatine, fibrin, or 

 other protein. 



By filtration through a Chamberland porcelain filter 

 the bacteria can be removed without destroying the 

 enzymes which they may have secreted ; this method 

 is very generally adopted in the study of bacterial 

 enzymes. 



Another plan is to destroy the vitality of the organ 

 isms by heat ; but as most enzymes are decomposed or 

 their powers greatly diminished at 65 to 70 C. a tem- 

 perature which is insufficient to kill many forms of 

 bacteria the method is unsatisfactory or only of limited 

 application. 



A simpler device, and one which is of general use, is 

 to treat the culture with an antiseptic substance of 

 sufficient strength to inhibit the growth of bacteria 

 without affecting the enzyme present. The compounds 

 best serving this purpose are toluene, phenol, thymol, 

 and salicylic acid ; chloroform is also useful, but is 

 volatile at somewhat low temperatures. 

 J3x. 56. Inoculate two or three tubes of nutrient broth with 



