40 BACTERIOLOGY 



The Production of Proteolytic Enzymes 



Certain bacteria produce enzymes which have the power of 

 ■converting proteids into propeptones^and peptones. Such a pro- 

 cess takes place in the liquefaction of gelatin and blood serum, 

 and in the peptonization of milk. To study the process, use as a 

 culture medium either blood serum or milk which has been 

 freed of its fat by passing through an unglazed porcelain filter. 

 Since serum is a more difficult material to obtain in an aseptic 

 condition, milk will serve as a better medium. This should be 

 perfectly fresh. The porcelain filter should be sterilized for 

 one-half an hour in an autoclave under a pressure of 5-10 

 pounds. The milk serum or filtrate can thus be obtained per- 

 fectly aseptic. Fifty cubic centimetres of this serum placed in 

 a sterile flask is then inoculated with a culture and kept at the 

 optimum temperature for 10 days. To 40 cc. of the culture add 

 60 g. of ammonium sulphate, and warm to 50° C. for one-half an 

 hour. This will precipitate all the proteid bodies except the 

 peptones. Filter ; the filtrate will contain the peptones and 

 propeptones. To test their presence add to a portion of the 

 filtrate enough caustic potash solution to make strongly alkaline, 

 and then a few drops of a i per cent solution of copper sulphate. 

 A violet color indicates the. presence of peptones. 



The Production of Diastatic Ferments 



Certain bacteria produce enzymes which have the property of 

 converting starch into sugar. To test their presence, the follow- 

 ing method is recommended : Inoculate a few tubes of bouillon, 

 free from sugar, with the organism to be tested, and incubate 

 for 10 days. Prepare a thin starch paste, to which is added 

 2 per cent of thymol. The latter must be free from sugar. 

 Mix equal parts of the broth culture and the above paste, and 

 place in a thermostat for 6-8 hours. Filter, and test filtrate 

 with Fehling's solution for sugar. 



