20 APPLIED BACTERIOLOGY FOR NURSES 



that certain of the light rays exert a destructive action 

 on bacteria. In fact, so resistant a germ as the tubercle 

 bacillus may be killed by several hours' exposure to 

 direct sunlight. 



So far as the -effect of oxygen on the growth of bac- 

 teria is concerned, it is interesting to note that there are 

 three large classes of bacteria, namely, those which 

 require oxygen for their growth, those which will not 

 grow if oxygen is present, and those which will grow 



Fig. 6. Novy's jars for anaerobic cultures. 



whether oxygen is present or absent. The bacteria 

 belonging to the first class are called aerobes, those 

 belonging to the second class are anaerobes, and those 

 belonging to the third class are calledfacultative anaerobes. 

 The bacillus of diphtheria is an aerobe, so is that of 

 tuberculosis; the bacillus of tetanus and that of malig- 

 nant edema are anaerobes; the colon bacillus and the 

 bacillus of anthrax are facultative anaerobes. Anaerobic 

 cultures are conveniently grown in an atmosphere of 

 hydrogen in a Novy jar, or they may be grown in an 



