PHOSPHORESCENCE OR PHOTOGENESIS 97 



PRODUCTION OF "AROMATIC" COMPOUNDS. 



These have been mentioned in discussing the putrefac- 

 tion of proteins, as indol, skatol, phenol and various cresols. 

 Of these only the first is ordinarily tested for in the study 

 of bacteria, though others of the group become of value in 

 certain special cases. 



Fig. 66. — Culture of phosphorescent bacteria in an Ehrlenmeyer flask 

 photographed by their own light. Time of exposure twelve hours. (Molisch 

 from Lafar.) 



PHOSPHORESCENCE OR PHOTOGENESIS. 



This is a most interesting phenomenon associated with 

 the growth of some bacteria. The "fox fire" frequently 

 seen on decaying wood which is covered with a slimy deposit 

 is most commonly due to bacteria, though also to other fungi. 

 Phosphorescent bacteria are very common in sea water, 

 7 



