THE SAPROGENIC AND SAPROPHILIC BACTERIA 217 



saprogenic bacteria. B. vulgaris Mig. is a typical example 

 of this class. All putrefactive processes are brought about 

 by the action of bacterial enzymes. These enzymes are, in 

 the main, proteolytic. There are still other bacteria which 

 derive nutriment from and perhaps in some cases aid in break- 

 ing up still further the compounds formed by the saprogenic 

 bacteria. These organisms are called saprophilic bacteria. 

 B. coli, Sp. undula, and B. subtilis are examples of bacteria 

 which belong to this last-mentioned class. 



The saprogenic bacteria are very widely distributed. The 

 enzyme action of the saprogenic species undoubtedly serves 

 these organisms as a source of energy. It was supposed dur- 

 ing the early days of bacteriological research that decompo- 

 sition was due to one species of bacteria which was called 

 Bacterium termo. It is now known that putrefaction is due 

 to a large number of species of saprophytic bacteria. These 

 bacteria are not always found under the same conditions. 

 No attempt has been made to classify the putrefactive bac- 

 teria. It seems that some species are particularly common 

 in decomposing animal material, others in decomposing 

 vegetable material, and others in decomposing urea. 



Proteolytic Enzymes. The proteolytic enzymes of bac- 

 teria resemble in their action the trypsin of the pancreatic 

 juice of the animal body in many particulars. These enzymes 

 act better in an alkaline than in an acid medium. There is a 

 proteolytic enyzme which is secreted by a large variety of 

 bacteria which dissolves or peptonizes gelatin compounds. 



