LUMINOUS BACTERIA. 293 



cause this phenomenon arc caUcd 2Iicrococciis phosplioriis. 

 The\' are minute spherical or ovoid cells whose diameter 

 does not exceed one or two thousandths of a millimeter. 

 At a temperature of from nine to twelve above zero 

 these oro-anisms shine so bricrhtl}' that their phosphores- 

 cence can be seen even in the day time in the diffused 

 light of a room. They are ver-s' sensitive to higher 

 temperatures, and about 30" suffices to kill them. These 

 bacteria therefore could hardh' exist in our bodies. 

 They have been photographed b^- their own light. Like 

 the phosphorescent fungi they shine without intermission, 

 while the luminous organisms in the sea shine onh' when 

 \\\<t\ are irritated. Hence the shock of a stone thrown 

 into the sea causes this light-reaction in these lower 

 organisms. The sudden illumination of these organisms 

 when irritated may be protective and intended to terrify 

 the approaching cnem\-. But this light must have other 

 advantages for those creatures which li\'e in the ocean 

 depths ; it must facilitate their (_|uest for food. 



In all luminous creatures the emission of light is 

 associated with lile and disappears at death. In spite 

 of this the phi,-siologist Raphael Dubois has succeeded 

 in extracting the luminous substance produced in abun- 

 dance b\' certain molluscs, the so called "Sea-dates'' 

 (PJiolas dacfvJus). It had long been known that the 

 hands and mouths of those eating these molluscs became 

 phosphorescent. From this luminous substance Raphael 

 Dubois made crystalline "Luciferin", and a ferment 

 called "Luciferase" ; and when he mixed these the 

 solution pliosphoresced. Raphael Dubois and Mollisch 



