THE BIOLOGICAL ACTIVITIES OF BACTERIA 49 



able for bacterial development. Thus, as is well known, freezing, 

 sterilizing by heat, or the addition of disinfectants will prevent the 

 rotting of organic material. 



In the laboratory, the presence of proteolytic enzymes is deter- 

 mined chiefly by the power of bacteria to liquefy gelatin, fibrin, or 

 coagulated blood serum. These ferments are not always secretions 

 from the bacterial cell, but in some cases may be closely bound to 

 the cell-body and separable only by extraction after death. In such 

 cases they are spoken of as endoenzymes. Whenever they are true 

 secretory products, however, they can be obtained separate from 

 the microorganisms which form them by filtration through a Berke- 

 feld candle. From such filtrates they may, in some cases, be obtained 

 in the dry state by precipitation with alcohol. When obtained in 

 this way the precipitated enzyme is usually much more thermostable 

 than when in solution, for while soluble enzymes in filtrates are 

 usually destroyed by 70 C., and even less, the dried powder may 

 occasionally withstand 140 C. for as long as ten minutes. 3 



Apart from the general conditions of temperature and moisture, 

 the development of these enzymes seems to depend directly upon the 

 presence of proteins in the culture media. The number of bacterial 

 species which produce proteolytic enzymes is legion. Among those 

 more commonly met with are staphylococci, B. subtilis, B. proteus, B. 

 faecalis liquefaciens, Spirillum choleras asiaticae, B. anthracis, B. 

 tetani, B. pyocyaneus, and a large number of others. The inability 

 of any given microorganism to liquefy gelatin or fibrin by no means 

 entirely excludes the formation by it of proteolytic enzymes, since 

 these ferments may often be active for one particular class of protein 

 only. 



In order to study the qualitative and quantitative powers of any 

 given bacterial proteolyzing enzyme or protease, it is, of course, 

 necessary to study these processes in pure culture in the test tube 

 with media of known composition. In the refuse heap, in sewage, or 

 in rotting excreta, the process is an extremely complicated one, for 

 besides the bacteria which attack the protein molecule itself, there 

 are many other species supplementing these and each other, one 

 species attacking the more or less complex end-products left by the 

 action of the others. 



Exactly what the chemical reactions are which take place in these 



* Fuhrmann, "Die Bakterienzyme, ' ; p. 45. 



