1 70 GENERAL PHYSIOLOGY 



of light, as in phosphorescence. This characteristic is com- 

 mon in various forms of life, particularly in marine animal 

 forms among the photobacteria. These are saprophytes 

 which live in salt water and grow especially on peptones, such 

 as are common in dead fish. They produce light only in the 

 presence of oxygen, and the phenomenon of phosphorescence 

 is intimately associated with respiration. The energy ob- 

 tained as a result of respiration shows itself also in motion, 

 and a good example of this is frequently seen in hanging- 

 drop preparation, where the aerobic bacteria lose their power 

 of motion when free access to the oxygen of the air is denied 

 them. 



