PATHOGENIC BACTERIA 



229 



saprophytes. As examples of this last-mentioned class of 

 bacteria, Msp. comma and B. typhosus maybe given. Bacteria 

 of this class are called facultative saprophytes. 



There are other species of bacteria which are not able to 



FIG. 46. Bact. tuberculosis in human lung. After Muir and Ritchie. 



exist for any length of time outside of the bodies of the animal 

 which they infect. These bacteria are called strict or obligate 

 parasites. Bact. tuberculosis and Bact. leprae are examples 

 of this class. It should be noted in this connection that 

 bacteriologists have been able to cultivate some of these strict 

 parasites on special artificial media which is made to resemble, 



