36 MICROBIOLOGY 



always closely drawn the term "parasitic" bacteria is often 

 used synonymously with "pathogenic" bacteria. 



Pathogenic bacteria. These are bacteria capable of 

 living in the tissues of animals and as a result of their pres- 

 ence and multiplication produce more or less disturbance in 

 the animal economy. This disturbance is the disease which 

 they produce. 



Kruse * in his discussion of saprophytic and pathogenic 

 bacteria has divided them in the following manner: 



I. Saprophytes (not infectious bacteria). 



1. not toxic bacteria. 



2. toxic bacteria. 



II. Parasites (infectious or virulent bacteria). 



1. Bacteria which cause local infection. 



a. slight growth, strong toxin formation. 



b. strong growth in the depths of the tissue. 



c. strong growth on the surface. 



2. Bacteria which cause general infection. 



a. by continuous growth in the tissues. 



b. by metastasis. 



c. septicemia. 



Zymogenic bacteria. These are bacteria which cause 

 fermentation of the carbohydrates. 



Saprogenic bacteria. These are bacteria which cause 

 putrefaction and decomposition of organic matter, usually 

 animal tissue. 



Chromogenic bacteria. These are bacteria which pro- 

 duce pigment in the growth itself on a solid medium or im- 

 part color to the medium in or on which they are multiplying. 



Photogenic bacteria. These are bacteria which cause 

 phosphorescence. 



Aerogenic bacteria. These are bacteria which produce 

 gas as the result of the fermentation of the substance in 

 which they are growing. 



* Kruse. In Fliigge's Die Mikroorganismen. Bd. I, p. 276. 



