144 EDWIN O. JORDAN 



factors are of much greater influence than the presence of gelatin in 

 determining the generation of liquefying enzymes. 



2. In simple non-proteid solutions of asparagin, lactose, and 

 mineral salts (sodium phosphate and magnesium sulphate) gelatinase 

 is produced by some bacterial species quite as abundantly, although 

 generally not as rapidly, as in nutrient broth or gelatin. Lactose is 

 more favorable than dextrose to gelatinase production. 



3. The reaction of the culture medium is, at least in some cases, 

 without apparent effect upon the enzyme production except as it 

 affects the conditions of bacterial growth. 



4. The heat resistance of the gelatinase, as this is determined by 

 heating the ordinary fluid culture, is conditioned by a variety of influ- 

 ences. One of these is the reaction of the medium. The gelatin- 

 liquefying enzymes produced by a number of microorganisms endure 

 heat very much better when heated in an acid than in an alkaline or 

 a neutral medium. The usual tests of heat resistance of bacterial 

 enzymes which are made directly with the culture in which the 

 enzymes are produced have little value. 



5. Some, at least, of the bacterial gelatinases pass through the 

 Berkefeld filter without weakening. 



6. The reaction most favorable to the manifestation of gelatino- 

 lytic activity is different in different cases. The enzymes produced 

 by some species act most rapidly in a medium slightly acid to phenol- 

 phthalein, while others do best with an alkaline reaction. It can no 

 longer be maintained that an initial alkaline reaction affords the opti- 

 mum condition for all bacterial proteolytic enzymes. 



7. The enzymes that have been experimented with act more ener- 

 getically at 45 C. than at lower temperatures. They may continue 

 to be effective at temperatures as high as 60. 



8. Some bacterial enzymes manifest their activity at temperatures 

 considerably above the thermal death-point of the organism produ- 

 cing them. 



9. The gelatin liquefied by some cultures of bacteria is hardened 

 by formalin. This, however, is true chiefly in the case of young cul- 

 tures, of cultures grown at room temperature, and of feeble strains. 

 No difference, such as alleged by Mavrojannis, exists between different 

 species. The stage of liquefaction in which formalin produces 



