66 THE NATURE OF ANIMAL LIGHT 



of photobacteria gave 6.8 X 10"* German-normal candles, 

 about ten times Lode's value. Even at this rate commer- 

 cial lighting by luminous bacteria does not appear a 

 promising field for investors. 



To sum up, we may say that light from animal sources 

 is in no way different from light of ordinary sources, ex- 

 cept in intensity and spectral extent. It is all visible light, 

 containing no infra-red or ultra-violet radiation or rays 

 which are capable of penetrating opaque objects. It is not 

 polarized as produced, but may be polarized by passing 

 through a Nichol prism. Like ordinary light, animal light 

 will also cause fluorescence and phosphorescence of sub- 

 stances, affect a photographic plate, cause marked helio- 

 tropism of plant seedlings (Nadson, 1903) and stimulate 

 the formation of chlorophyll (Issatschenko, 1903, 1907). 

 Because of the weakness of bacterial light, etiolated seed- 

 lings do not become green to the eye (Molisch, 1912 book), 

 but a small amount of chlorophyll is formed which can be 

 recognized by the spectroscope because of its absorp- 

 tion bands. 



