PHOTOGENIC BACTERIA 199 



microorganisms (non-photogenic) which generate inflamma- 

 ble gases, such as phosphoretted hydrogen and methane. 



Some vegetables, such as potatoes, beans, etc., on decompo- 

 sition may give off light and show the presence of phosphor- 

 escent bacteria. Decomposing meats, particularly sausages 

 and fish, also may be covered with different species of phos- 

 phorescent bacteria. 



Food Requirements. As stated above, all the photogenic 

 bacteria which occur in water are marine. On cultivation of 

 these bacteria it is therefore necessary for the media to contain 

 two to three per cent sodium chloride in addition to other 

 salts, peptone,, and some carbon compound such as sugar 

 or glycerine. 



Magnesium, potassium and calcium chloride, potassium 

 sulphate, stimulate the production of light by bacteria. 

 Gorham states that he has been able to grow phosphorescent 

 bacteria on purely synthetic media. 



Fischer states that the phosphorescence of the sea is due to 

 the growth of saprophytic photogenic bacteria on dead sea 

 animals and the subsequent washing off of these forms in 

 large numbers by the waves. 



Hans Molisch in " Leuchtende Pflanzen " reports the isola- 

 tion of twenty-six species of photogenic bacteria. He states 

 that the flesh of cattle (48 per cent of the samples examined) 

 and salt water fish (100 per cent of the samples examined) on 

 exposure to the air show phosphorescence, and the photogenic 

 bacteria can be isolated. Fresh water fish seldom if ever show 



